Shared leave,happier parent couples? Parental leave and relationship satisfaction in Germany

Abstract

This study investigates how parental leave policies and uptake may impact heterosexual couples’ relationship satisfaction. It focuses on Germany as an example of a country with a history of familialist policies and long maternal leaves that has recently undergone a significant policy shift. We extend the literature by examining the effects of maternal and paternal leave duration on both partners’ relationship satisfaction while distinguishing between the length of solo, joint and overall leave. The study applies two different methods on data from the Panel Analysis of Intimate Relationships and Family Dynamics (pairfam). First, the study applies fixed-effects regression models (n = 1046 couples) to investigate the impact of parental leave duration on the change in mothers’ and fathers’ satisfaction over the child’s early years. Second, drawing on exogenous variation as a result of the parental leave reform of 2007, which shortened paid leave for mothers and incentivised fathers’ leave take-up, difference-in-difference analyses (n = 1403 couples) analyse reform effects on relationship satisfaction of parents with 3-year-old children. The fixed-effects models indicated a consistent negative impact of maternal – especially solo – leave duration on both mothers’ and fathers’ relationship satisfaction. No significant effects of paternal leave length were found. The difference-in-difference approach revealed a positive reform effect on mothers’ relationship satisfaction. In combination, these results suggest that the reduction in maternal leave as part of the reform has had a greater impact on couples’ relationship quality than the relatively short duration of leave taken by most fathers after the introduction of the individual leave entitlement.

Keywords

family policy parental leave relationship quality parenthood relationship satisfaction couple relationships Germany fathering gender

Introduction

This study investigates how parental leave policies and uptake relate to heterosexual couples’ relationship satisfaction. Couples’ relationship quality tends to deteriorate after the transition to parenthood and while children are young (Twenge et al., 2003). Recent conceptualisations of the incomplete gender revolution (Esping-Andersen and Billari, 2015; Goldscheider et al., 2015) have argued that gender inequity and inequality in the division of paid and domestic work within couples are likely to contribute to greater dissatisfaction with relationships, especially among women, and to increase relationship instability. This is supported by a few empirical studies from the US and the UK providing evidence that a more equal division of childcare improves couples’ relationship satisfaction (Carlson et al., 2011; Schober, 2012). In Germany, in contrast, couples with a traditional division of labour exhibited greater stability up until the early 2000s (Cooke, 2004). These new frameworks (Esping-Andersen and Billari, 2015; Goldscheider et al., 2015) also point to the importance of institutions for supporting the diffusion of gender egalitarian norms in order to advance towards completing the gender revolution. Cross-nationally, it has been shown that parental happiness heavily depends on the availability and generosity of parental leave policies (Glass et al., 2016). In particular, parental leave policies that incentivise fathers’ uptake of leave and support mothers’ labour market return by providing relatively well-paid leave of moderate duration have been found to promote a more equal division of childcare and paid work (Hook, 2006; Patnaik, 2019; Pettit and Hook, 2005; Pronzato, 2009; Ray et al., 2010; Schober, 2014). To date, little evidence exists as to a more direct relationship between parental leave and relationship satisfaction among parent couples outside the US context. The present article aims to shed light on the effects of parental leave in a European context with relatively generous, yet historically familialist policies. We explore the impact of Germany’s parental leave reform in 2007, which marked a dramatic shift in national family policy, on couples’ relationship satisfaction. Furthermore, we examine at the individual level how the division of leave between parents relates to changes in mothers’ and fathers’ relationship satisfaction in families in which both parents remain romantically involved with one another. With respect to gender revolution theory, this provides relevant evidence on how parental leave policies that support greater gender equality may impact relationship quality and ultimately also stability. In 2019, fewer than half of European Union countries offered well-paid parental leave and had also adopted some type of bonus leave entitlement to encourage fathers to take parental leave (Koslowski et al., 2019). However, in August 2019, the EU Work–Life Balance Directive came into force, which inter alia requires all EU member states to introduce at least 10 days of paternity leave and at least 2 months of non-transferable paid parental leave for each parent. Therefore, in the near future, other EU member states are increasingly likely to implement parental leave reforms containing similar measures as those introduced in Germany over the past 15 years.

Institutional context

In the past, the German family policy model has frequently been classified as supported or explicit familialism (Hook, 2015; Leitner, 2003), which is seen as suppressing employment of second earners and reinforcing gender inequality. Until the mid-2000s, parental leave entitlements in Germany were rather long and low-paid. Parents had the right to take leave until the child’s third birthday. Until 2006, mothers or fathers on leave were entitled to a child-rearing benefit of about €300 per month for the first 6 months. After 6 months, benefits were reduced on a sliding scale based on household income. Families could receive the child-rearing benefit for up to 24 months. The parental leave reform in 2007 (‘Elterngeldreform’) implemented an income-based benefit of between 65 and 100 percent of net earnings for 12 months (capped at €1800 per month). Two additional months of leave are awarded to the couple if each partner takes at least 2 months of parental leave (BMFSFJ, 2008). As in most families, mothers stay at home for 12 months, whereas the vast majority of fathers take only these minimum 2 months in order to receive the bonus, the latter are frequently known in Germany as ‘daddy months’ (Wrohlich et al., 2012). In 2015, ‘Elterngeld plus’ was implemented, which incentivises parents to work part-time and receive half of the parental leave benefits to which they would be entitled for double the time (Huebener et al., 2016). Furthermore, 4 months of extended benefit entitlements were introduced for couples where both parents simultaneously work long part-time hours while on parental leave. The provision of early childhood education and care services has also expanded massively since the mid-2000s (Stahl and Schober, 2018). In light of these new reforms, the current German family policy model may be better described as optional familialism (Leitner, 2003; Stahl and Schober, 2018). It combines familialist support in the form of joint taxation and the option to take long job-protected leave with defamilialist policies of shorter but relatively well-paid leave and entitlement to formal early childcare.

Research gap

Several evaluation studies of the 2007 parental leave reform in Germany showed that it increased paternal leave uptake and childcare involvement, as well as mothers’ intentions to return to work and actual employment in the second year after birth (Kluve and Tamm, 2013; Schober, 2014; Wrohlich et al., 2012; Ziefle and Gangl, 2014). Since the reform, fathers increased their leave uptake from less than 3 percent before 2007 to about 10 percent in 2007 and 2008 (Wrohlich et al., 2012); subsequently, uptake kept growing steadily, reaching 39 percent for births in 2016 (Statistisches Bundesamt, 2020). Nevertheless, 75 percent of fathers who took some leave recently still took no more than their individual entitlement of 2 months.

Myrskylä and Margolis (2013) found that the 2007 reform increased parental life satisfaction and reduced the frequently observed decline in happiness in the years following first childbirth. Their evaluation revealed relatively homogeneous positive effects across various population groups, which were significantly larger for mothers than fathers. Their analyses also indicated that the effects were partly due to smaller reductions in household incomes and satisfaction with income after the reform. To date, the effects of this German reform on relationship satisfaction have not been assessed. For Norway, Kotsadam and Finseraas (2011) found that after the introduction of an individual leave entitlement for fathers of 4 weeks in 1993, couples reported a more gender-equal division of household labour and reduced within-couple conflicts over housework.

Two recent US studies investigating fathers’ uptake of paternity leave after childbirth found positive associations with couples’ reported relationship satisfaction (Petts and Knoester, 2019, 2020). Petts and Knoester (2019) reported a strong effect of paternal leave on mothers’ happiness with their relationship, which accounted for the overall increase in couples’ relationship satisfaction up to 5 years after birth. In a second study, (longer) paternal leave was associated with increased relationship satisfaction among mothers and with reduced relationship conflict among employed mothers only (Petts and Knoester, 2020). To reduce the risk of selection bias resulting in the fact that US fathers who are entitled to leave after childbirth are a selective group, both studies applied propensity score matching and augmented inverse propensity weighting. A recent Korean study (Kramer et al., 2019) found that paternity leave uptake after childbirth among Korean fathers predicted greater satisfaction with their job and life overall, which was indirectly associated with improved satisfaction with family relations among mothers up to 3 years after birth. Interestingly, no direct effect on mothers’ satisfaction was found. This study applied time-lagged actor–partner interdependence models and instrumental variables to reduce the risk of selective paternity leave uptake biasing the results. Due to the short paternity leave entitlement in Korea and as the majority of US fathers took only one week off or less (Petts and Knoester, 2019, 2020), these existing studies from the US and Korea investigated effects of relatively short leaves by fathers right after childbirth in combination with very limited entitlements to paid parental leave for mothers in both countries (Koslowski et al., 2019). In comparison, this study focuses on leaves of relatively long duration taken by mothers and the somewhat longer leave typical of ‘daddy months’, which are characteristic of an increasing number of European countries with relatively generous leave policies.

We extend previous studies by combining the assessment of a parental leave reform in Germany with a longitudinal individual-level analysis of changes in couples’ relationship satisfaction after parental leave onset. First, we explore the relationship between leave-taking and relationship satisfaction in more detail by applying fixed-effects panel models. Here, we extend earlier research by considering the actual length of leave taken and whether it was taken solo or jointly. Second, by implementing a difference-in-means (DiM) and difference-in-difference (DiD) design, we examine the medium-term effects of the 2007 parental leave reform on relationship satisfaction in couples when their children were about 3 years old. By combining the strengths of two statistical methods, we are able to provide new evidence of the effects of parental leave policies on couples’ relationship satisfaction that are highly relevant to policymakers in Germany and other European countries increasingly orienting themselves towards Nordic-style leave policies.

Conceptual framework and hypotheses

We draw on role theory to frame our understanding of how fathers’ uptake of parental leave after childbirth might be related to mothers’ and fathers’ relationship satisfaction (Goode, 1960; Hecht, 2001). After childbirth, parents are frequently faced with different role demands as mother and father, income-earner, and loving partner. According to role theory, role conflict as a result of multiple conflicting roles, or role overload, defined as stress from too many responsibilities, can lead to declines in relationship quality and satisfaction (Dew and Wilcox, 2011; Hecht, 2001; Twenge et al., 2003). In line with family system theory (Broderick, 1993; Brown, 1999), we understand families as interconnected and interdependent systems and assume positive or negative effects of leave-taking on one partner to cross over to the other partner.

During the early years after childbirth, most mothers in Germany are primarily responsible for childcare and domestic duties, whereas fathers’ domestic contributions increase much less (Schober and Zoch, 2019). This role traditionalisation may increase perceptions of unfairness, role conflict, and role overload, especially for mothers with egalitarian ideologies and career ambitions (Yavorsky et al., 2015). Role traditionalisation also often leads fathers to feel detached from family life (for example, Chalmers and Meyer, 1996). Given the increasingly egalitarian ideals in post-industrial societies (Knight and Brinton, 2017), greater childcare involvement by fathers has been found to positively relate to mothers’ and fathers’ reports of relationship quality within couples (Carlson et al., 2011, 2016; Schober, 2012). Several longitudinal studies have found that fathers who took some leave increased their childcare and housework time more and continued to be more involved after the end of their leave period (Bünning, 2015; Schober and Zoch, 2019). We expect this greater paternal involvement to reduce the workload for mothers. Fathers who took leave also reported greater satisfaction regarding contact with their children (Haas and Hwang, 2008). In addition, qualitative studies showed that fathers who took several weeks of parental leave experienced a cultural shift in their definition of fatherhood and participated more in interactions within family life (Henwood and Procter, 2003; Rehel, 2014). We therefore formulate the following hypothesis:

H1: Leave uptake and longer leaves by fathers are positively associated with improved relationship satisfaction of fathers (H1a) and mothers (H1b) during the first years after birth.

While joint leave might enhance both partners’ perceived relationship satisfaction as a result of shared experiences of co-parenting and greater mutual feelings of security, confidence, and support in family life, taking solo leave may strengthen fathers’ feeling of inclusion in family life in a phase that is usually strongly mother-dominated (Craig, 2006). In Germany, couples in which fathers take parental leave are still a selective group: they are disproportionately highly educated, hold egalitarian gender beliefs, or consist of women who earn more than their partners (Pfahl and Reuyß, 2009; Trappe, 2013). Given the restricted sample of fathers who take leave and the limited variation in gender ideologies in this group in our data, we are unable to examine variations depending on fathers’ or mothers’ gender ideologies.

The consequences of variation in the duration of mothers’ parental leave for relationship satisfaction are more ambiguous. Whereas longer full-time leave might allow mothers to concentrate on family care and reduce role conflict and overload, the relatively long leaves of mothers in Germany of about a year or more have been shown to reinforce a traditional gender division of domestic work even after mothers’ labour market return (Schober and Zoch, 2019). In particular, such long periods of solo leave by mothers may reduce fathers’ integration into family life, inhibit close father–child bonds and reduce mothers’ and fathers’ shared experiences. Whereas the former mechanism may benefit both partners’ relationship satisfaction, the latter may reduce the couple’s emotional closeness and relationship quality. We therefore formulate competing hypotheses regarding the association between mothers’ parental leave duration and relationship satisfaction in couples:

H2a: Longer durations of maternal leave are associated with improved relationship satisfaction in the first years after the child’s birth.

H2b: Longer durations of solo maternal leave are associated with lower relationship satisfaction in the first years after the child’s birth.

Potential positive effects of longer leaves by mothers are likely to be stronger for mothers with more traditional gender beliefs, as a more traditional division of childcare is more likely to be in line with their own gender ideologies and parenting ideals. By contrast, the potential negative effects are likely to be stronger for mothers who aspire to more egalitarian relationships and a more egalitarian division of labour with their partners. This leads us to formulate Hypothesis 3:

H3: The positive (negative) effects of longer maternal leave on mothers’ relationship satisfaction are expected to be weaker (stronger) for mothers with more egalitarian gender ideologies compared to mothers with more traditional gender beliefs.

On the whole, we expect that the parental leave policy reform in 2007 expanded couples’ options as to how to distribute parental leave between mothers and fathers. The uptake incentive for fathers and the more generous parental leave benefit gave parents the chance to decide more deliberately how to divide paid and family work. The expected positive effects of fathers’ leave uptake in combination with some potential positive effects of mothers’ shorter leaves on both mothers’ and fathers’ relationship satisfaction are likely to outweigh any negative effects of mothers’ faster labour market re-entry. As a result, we expect an overall positive effect on couples’ relationship quality, as summarised in Hypothesis 4:

H4: Mothers and fathers who had their children after the parental leave reform in 2007 will report higher medium-term relationship satisfaction than parents who had their children before the reform.

Data and measures

Data, analytical strategy, and sample selection

Data

For our analyses, we used Waves 1 to 8 (2008/09 to 2015/16) of the Panel Analysis of Intimate Relationships and Family Dynamics (pairfam, https://www.pairfam.de/en/). The annual panel survey started in 2008/09 and included 12,000 randomly selected individuals living in private households in Germany. All main respondents belong to one of three birth cohorts: 1971–1973, 1981–1983, or 1991–1993 (Brüderl et al., 2017). Despite the lack of coverage before the reform in 2007, the pairfam data set contains the most suitable longitudinal information on parental leave and relationship satisfaction in Germany.

Analytical strategy and sample selection

To examine individual-level relationships between mothers’ and fathers’ uptake of parental leave and changes in relationship satisfaction over the first years after childbirth (Hypotheses 1–3), we implemented fixed-effects panel models. These allow us to investigate within-person effects and control for time-invariant unobserved individual characteristics that may correlate with parental leave uptake and relationship satisfaction. As presented in equation (1), we measured the within-person associations between variations in mothers’ and fathers’ leave-taking Leave_it and variations in their relationship satisfaction y_it over time. x_it comprises a vector of all time-varying control variables at the individual and household level. The indicator ε_it represents random variation at each time point and u_i captures the unobserved time-invariant individual effect on the dependent variable.

y_{i t} = β_{1 t} + β_{2} L e a v e_{i t} + β_{3} x_{i t} + ε_{it} + u_{i}

(1)

We estimated models differentiating between the amount of total leave by the mother, total leave by the father, solo leave by the mother, solo leave by the father, and joint leave by both parents together. As we expected mothers’ gender ideologies to moderate the effects of their own leave-taking, we estimated additional models with interaction effects between mothers’ gender ideologies and duration of total and solo leave, respectively. Due to data limitations, we were unable to measure unpaid and part-time leave. However, we controlled for mothers’ employment status in the final modelling step. The standard error estimation in the fixed-effects panel regression models accounts for the nested data structure of time points being nested within individuals.

For the fixed-effect panel models, we had to restrict the sample to intact heterosexual couples who had at least one child during the observation period. For a small number of respondents with several partnership periods with changing partners (n = 19), we examined the longest partnership. We used listwise deletion to exclude individuals with missing items. As fixed-effect models require repeated observations, we deleted all couples who only appeared in one wave and ended up with a final sample size of 1046 couples and 4115 observations. On average, we observed couples for 3.9 waves, with a minimum of 2 waves and a maximum of 7 waves. At the end of the observation period, 27 percent had one child, 52 percent had two children and 21 percent had three or more children. We conducted additional robustness checks by lagging the leave duration variables by one year. For these analyses, the sample was slightly smaller with 913 couples and 2452 observations.

To examine the overall effects of the parental leave reform that came into effect in January 2007, as planned for Hypothesis 4, we applied a DiD approach. In a first exploratory step, we estimated a DiM model using pooled OLS regression (equation (2)). We differentiated between parents with children born in 2006 (pre-reform) and parents with children born in 2007 (post-reform) and compared their relationship satisfaction based on the interviews when the children were between 3 and 4 years old (the year of data collection ranged from 2008 to 2011). As data collection started in 2008 after the reform, we can only estimate medium-term effects when children are 3 years old. In Germany, parents have a right to return to their previous job until the child is 3 years old, even though parental leave benefits expire usually in the second year after birth. Focussing on the interview when children are between 3 and 4 years old allows us to examine whether any effects persist after most parents have re-entered the labour market. Control variables to account for differences in group composition are depicted by the vector x_i, while e_i denotes the error term.

y_{i} = β_{0} + β_{1} P o s t ‐ r e f o r m_{i} + β_{2} x_{i} + e_{i}

(2)

Because DiM analysis might overlook time trends in relationship satisfaction unrelated to the reform, we focus on the estimation of DiD models, as depicted in equation (3).

y_{i t} = β_{0} + β_{1} T r e a t m e n t_{i} + β_{2} P o s t ‐ r e f o r m_{t} + β_{3} {(T r e a t m e n t * P o s t ‐ r e f o r m)}_{it} + β_{4} x_{i t} + e_{i t}

(3)

Parents with 3-year-old children born pre-reform in 2006 or post-reform in 2007 represent the treatment group. They are compared with a control group of parents with children born in 2004 and 2005 who were aged between 5 and 6 years at the comparable time of the interviews between 2008 and 2011. The interaction term between post-reform and treatment group, indicated by β₃, compares the difference in mothers’ and fathers’ relationship satisfaction between those with children born in 2006 (pre-reform) and those born in 2007 (post-reform) with the difference in the time trend for the control group of parents with children born in 2004 compared to those born in 2005.

The sample for the DiD analysis was restricted to heterosexual couples with children. For the DiM and DiD models, we applied robust standard errors, as couples who had several children may be included in both the pre- and post-groups. Item non-response in the control variables was imputed using chained multiple imputations. The final sample included 776 couples for the DiM and 1403 couples for the DiD analysis.

Dependent variables

Each year, pairfam asked mothers and fathers ‘How satisfied are you with your relationship in general?’. Their answers, measured on an 11-point scale with 0 representing very unsatisfied and 10 very satisfied, provide the basis for our dependent variables representing fathers’ and mothers’ relationship satisfaction. Previous studies have shown that a single-item measure of marital satisfaction was reliably related to other measures of marital quality and daily intimacy (Laurenceau et al., 2005). Table 1 reveals a fairly high mean level of satisfaction of approximately 8 points for both samples.

Table 1.

Descriptive statistics: Means/shares of main study variables.

Variables in fixed-effect models		Mother		Father
Relationship satisfaction^a		8.35 (2.04)		8.41 (2.02)
Leave duration (months)		4.13 (4.84)		0.46 (1.37)
Solo leave duration (months)		4.03 (4.77)		0.37 (1.24)
Gender role ideology^b		3.69 (1.34)		3.36 (1.41)
Age of youngest child (years)		5.54 (4.40)		5.54 (4.40)
Number of children: One child		0.48		0.48
Number of children: Two or three		0.49		0.49
Number of children: Four and more		0.03		0.03
Relationship duration (months)		167.52 (70.65)		167.52 (70.65)
Household income (net, €1000)		2.97 (1.19)		2.97 (1.19)
Maternal employment: Not employed		0.45		0.45
Maternal employment: Part-time		0.28		0.28
Maternal employment: Full-time		0.27		0.27
Weekly working hours: Father		40.85 (14.13)		40.85 (14.13)
N couples/observations		1,046/4,115		1,046/4,115
Variables in diff.-in-diff. models	Pre-reform		Post-reform
	3-year-olds born 2006	5-year-olds born 2004	3-year-olds born 2007	5-year-olds born 2005
Fathers’ relationship satisfaction^a	8.51 (1.91)	8.09 (2.41)	8.45 (1.98)	8.53 (1.64)
Mothers’ relationship satisfaction^a	8.28 (2.15)	8.16 (2.32)	8.38 (1.96)	7.97 (2.48)
Number of children: One child	0.21	0.15	0.26	0.13
Number of children: Two or three	0.71	0.76	0.66	0.83
Number of children: Four and more	0.08	0.08	0.08	0.04
Relationship duration (months)	126.30 (63.90)	137.83 (64.45)	126.67 (66.34)	150.28 (64.35)
Household income (net, €1000)	2.85 (1.14)	3.19 (2.73)	2.96 (1.15)	3.13 (1.35)
Cohort born 1981-83 (Ref. 1971–73)	0.33	0.28	0.44	0.32
Region: East Germany (Ref. West)	0.21	0.27	0.40	0.38
N couples	133	123	167	116

Note. Standard deviations in parentheses. Source: pairfam, release 8.0.

^aRelationship satisfaction on a scale from 0 to 10.

^bGender role ideology: 0 = traditional, 5 = egalitarian.

Independent variables in the fixed-effects panel models

Paid parental leave uptake by mothers and fathers

Based on information on whether or not each parent took paid parental leave during each of the first 14 months after childbirth, we constructed two time-varying variables that indicate the total number of months of paid leave taken by mothers and fathers, respectively. We used continuous leave duration variables for fathers as well, as too few fathers took more than 2 months of leave to construct a categorical variable. We also conducted robustness checks with a binary variable indicating whether or not the father took any paid leave. The duration of fathers’ and mothers’ solo paid leave, defined as the time each took leave without their partner taking leave simultaneously, was calculated by subtracting the months of joint leave from the total leave taken. In our sample, 84 percent of mothers and 37 percent of fathers took paid parental leave for at least one of their children. In total, 226 fathers took paid leave and 180 chose at least 1 month of solo leave. Mothers who received parental leave benefits took on average 9.9 months (9.7 months of solo leave) in addition to the 2 months of mandatory maternity leave after birth. For fathers, the average length amounted to 2.1 months (2 months of solo leave).

Gender role ideologies

To test Hypothesis 3 regarding differential effects of maternal leave uptake depending on mothers’ gender role ideologies, we examined respondents’ agreement with the statement ‘a child under the age of six will suffer from having a working mother’, measured on a 5-point scale on which 1 represents fully disagree (egalitarian) and five fully agree (traditional). Mothers’ gender role ideologies were measured at the first observation for each person, either in the year before or in the year right after childbirth. We used a time-constant variable, as some women have been found to adapt their gender role ideologies to their actual gender division of labour practices after labour market return. We include an interaction between this continuous time-constant variable and maternal leave duration. Alternative binary and categorical specifications of this variable provided very similar results.

Control variables

In the fixed-effects panel models, we included time-varying indicators of couples’ relationship duration, youngest child’s age in years and months, and a categorical variable of the number of children in the household as control variables. The latter distinguished between (i) one child, (ii) two children, and (iii) three or more children to account for potentially larger changes after a first birth. In a final modelling step, we also accounted for variation in household income, mothers’ employment status and fathers’ working hours after the end of paid leave.

Independent variables in the difference-in-difference regression models

Parental leave reform

We constructed one dummy variable to distinguish the treatment group from the control group and another dummy variable to distinguish whether the groups were observed at the specific age of the child in the pre-reform period or in the post-reform period. Parents with 3-year-old children born pre-reform in 2006 or post-reform in 2007 represent the treatment group. They are compared with a control group of parents with 5-year-old children born in 2004 and 2005, respectively. The reform effect is estimated by interacting the treatment group dummy with the post-reform dummy variable.

Control variables

To control for compositional variations across groups not caused by the reform, we controlled for the main respondent’s birth cohort, household net income, relationship duration, number of children in the household, and whether the parents lived in the former East or West Germany. We did not control for maternal employment status, as this may act as a mediator variable of the reform impact on relationship satisfaction.

Multivariate analyses

Results

Fixed-effects panel models of fathers’ and mothers’ relationship satisfaction

We expected an improvement in relationship satisfaction among both fathers and mothers with increasing duration of fathers’ parental leave uptake (H1a and H1b). As depicted in Table 2, the duration of fathers’ leave was indeed associated with an increase in fathers’ relationship satisfaction, but the effect was small and only marginally statistically significant at the 10-percent level (Model 1). Consequently, a 1-month increase in overall paternal leave duration is associated with an improvement in fathers’ relationship satisfaction of 0.06 points on the 11-point satisfaction scale. Despite the very modest size of the effect, the results provide some support for Hypothesis 1a. When additionally distinguishing between fathers’ solo and joint leave in Model 2, both types of leave exhibited very similar associations as the total leave variable, but neither correlated significantly with changes in fathers’ relationship satisfaction. As shown in Model 3, paternal leave uptake was not significantly associated with changes in mothers’ relationship satisfaction, leading us to reject Hypothesis 1b.

Table 2.

Fixed-effects panel regression analyses predicting relationship satisfaction of fathers (models 1–2) and mothers (models 3–6).

	Father’s relationship satisfaction		Mother’s relationship satisfaction
Variable	Model 1	Model 2	Model 3	Model 4	Model 5	Model 6
Total duration of paid leave: Father	0.06†		−0.03
Total duration of paid leave: Father	(0.04)		(0.04)
Total duration of paid leave: Mother	−0.02**		−0.03**
Total duration of paid leave: Mother	(0.01)		(0.01)
Duration joint leave (months)		0.06		-0.04	-0.04	-0.04
Duration joint leave (months)		(0.09)		(0.09)	(0.09)	(0.09)
Duration solo leave: Father (months)		0.05		−0.03	−0.03	−0.02
Duration solo leave: Father (months)		(0.04)		(0.04)	(0.04)	(0.04)
Duration solo leave: Mother (months)		−0.02**		−0.03**	−0.04**	−0.03**
Duration solo leave: Mother (months)		(0.01)		(0.01)	(0.02)	(0.01)
Relationship duration (months)	−0.00	−0.00	−0.00	−0.00†	−0.00	−0.00†
Relationship duration (months)	(0.00)	(0.00)	(0.00)	(0.00)	(0.00)	(0.00)
Age of youngest child (years)	−0.01	−0.01	−0.01	−0.01	0.01	0.00
Age of youngest child (years)	(0.03)	(0.03)	(0.03)	(0.03)	(0.03)	(0.03)
Number of children: Two or three^a	−0.18	−0.18	−0.01	−0.00	−0.01	−0.03
Number of children: Two or three^a	(0.17)	(0.17)	(0.17)	(0.17)	(0.17)	(0.17)
Number of children: Four and more^a	0.17	0.18	0.45	0.45	0.53	0.40
Number of children: Four and more^a	(0.50)	(0.50)	(0.49)	(0.49)	(0.50)	(0.49)
Mother’s gender role ideology × mother’s solo leave duration^b					0.00
					(0.00)
Household income (net, €1000)						−0.01
Household income (net, €1000)						(0.01)
Maternal employment: Part-time^c						−0.17*
Maternal employment: Part-time^c						(0.10)
Maternal employment: Full-time^c						−0.16
Maternal employment: Full-time^c						(0.11)
Weekly working hours: Father						0.00
Weekly working hours: Father						(0.00)
Constant	9.35***	9.35***	9.17***	9.16***	9.17***	9.23***
Constant	(0.26)	(0.26)	(0.26)	(0.26)	(0.26)	(0.29)
N couple years	4115	4115	4115	4115	4115	4115
N couples	1046	1046	1046	1046	1046	1046
R² within	0.012	0.012	0.011	0.011	0.011	0.012

Note. Standard errors in parentheses. Source: pairfam, release 8.0.

*** p < 0.001, **p < 0.01, * p < 0.05, † p < 0.1.

^aRef: One child.

^bGender role ideology: 0 = traditional, 5 = egalitarian.

^cRef: not employed.

We formulated two competing hypotheses regarding potential effects of longer maternal paid leave uptake. On the one hand, Hypothesis 2a suggested that longer paid leave by mothers may be associated with improved relationship satisfaction for both partners in the first years after the child’s birth. On the other hand, Hypothesis 2b expected a negative association between longer maternal solo leave and relationship satisfaction. In Models 1 and 3, we observe statistically significant negative associations between longer total leave taken by mothers with relationship satisfaction among both mothers and fathers. In line with H2b, Models 2 and 4 show that this negative association is driven by longer solo leave by mothers. An increase in solo maternal leave of 4.8 months (one standard deviation) is associated with declines in mothers’ and fathers’ relationship satisfaction of 0.14 and 0.10 points, respectively, on the 11-point satisfaction scale (see also Online Appendix Figure 1). The length of joint leave does not significantly correlate with changes in relationship satisfaction among either mothers or fathers.

In Hypothesis 3, we assumed that the negative effects of maternal solo leave on mothers’ relationship satisfaction would be stronger for egalitarian-minded mothers. The non-significant interaction term between mothers’ solo leave duration with gender ideologies in Model 5, however, does not show any support for this hypothesis.

Difference-in-difference models to assess the overall impact of the parental leave reform

Table 3 shows the results of the DiM and DiD estimations. Hypothesis 4 assumed a positive effect of the parental leave reform on mothers’ and fathers’ relationship satisfaction. However, the first exploratory DiM models showed no significant differences in the satisfaction of parents with children born before compared to after the parental leave reform in 2007 (Models 1 and 2). The DiD estimates likewise revealed no significant effects of the reform on fathers’ relationship satisfaction (Model 3). However, for mothers, a highly significant positive interaction coefficient was found, which estimated the reform effect in terms of how much more relationship satisfaction increased for mothers in the treatment group compared to the control group since the pre-reform period (Model 4). In line with Hypothesis 4, these results indicate a positive effect of the parental leave reform on mothers’ relationship satisfaction. On average, the satisfaction of mothers with a child born after the reform was 0.76 units higher on the satisfaction scale (0–10) compared to mothers who had a child before the reform, while taking into account the time trend in relationship satisfaction of mothers in the control group. This is a sizable effect of about 40 percent of a standard deviation. The significant main effect of the post-reform coefficient suggests a decline in relationship satisfaction over time for the control group. This negative time trend explains the non-significant results of the DiM regression, as it probably masks the positive impact of the reform. Thus, the expected positive impact of the parental leave reform on relationship satisfaction (H4) was supported for satisfaction of mothers but not fathers.

Table 3.

Pooled OLS regression analyses for variables predicting fathers’ relationship satisfaction and mothers’ relationship satisfaction.

	Relationship satisfaction
Variable	Difference-in-means		Difference-in-difference
Variable	Father model 1	Mother model 2	Father model 3	Mother model 4
Post reform^a	−0.07	0.22	0.13	−0.51***
Post reform^a	(0.15)	(0.14)	(0.16)	(0.19)
Treatment group^b			0.19	−0.10
Treatment group^b			(0.17)	(0.17)
Post reform × treatment group^a,b			−0.13	0.76***
Post reform × treatment group^a,b			(0.22)	(0.24)
Cohort born 1981–83^c	0.78***	0.78***	0.54***	0.37*
Cohort born 1981–83^c	(0.19)	(0.19)	(0.16)	(0.19)
East Germany	0.01	−0.49***	−0.09	−0.14
East Germany	(0.15)	(0.18)	(0.12)	(0.14)
Relationship duration (months)	0.00***	0.00	0.00***	0.00**
Relationship duration (months)	(0.00)	(0.00)	(0.00)	(0.00)
Household income (net, €1000)	0.11**	0.20***	0.04	0.02
Household income (net, €1000)	(0.05)	(0.06)	(0.06)	(0.10)
Number of children: Two or three^d	−0.03	0.07	0.09	0.25
Number of children: Two or three^d	(0.14)	(0.14)	(0.19)	(0.23)
Number of children: Four and more^d	−0.95**	−0.56	−0.52**	−0.02
Number of children: Four and more^d	(0.41)	(0.34)	(0.25)	(0.27)
Constant	7.38***	7.25***	7.63***	7.66***
Constant	(0.30)	(0.38)	(0.34)	(0.46)
N observations/couples	776/736	776/736	1,403/1,297	1,403/1,297
F statistic	3.86***	7.11***	3.88***	3.38***

Note. Robust standard errors in parentheses. Source: pairfam, release 8.

*** p < 0.001, **p < 0.01, * p < 0.05, † p < 0.1.

^aPost reform: 3-year-olds born in 2007 and 5-year-olds born in 2005, Ref.: 3-year-olds born in 2006 and 5-year-olds born in 2004.

^b3-year-olds born in 2006 or 2007, Ref.: 5-year-olds born in 2004 or 2005.

^cRef: Cohort born 1971–73.

^dRef: One child.

Sensitivity analyses

To check the robustness of the results, we carried out several sensitivity analyses. For all the fixed-effects panel models, we reran the analyses including a dummy variable of whether the father took any leave or not instead of the continuous paternal leave duration variable. The paternal leave dummy did not reach statistical significance any more in the models of fathers’ relationship satisfaction, suggesting that, if anything, longer durations of leave are positively associated with improvements in fathers’ relationship satisfaction. For mothers’ relationship satisfaction, the results were unchanged and remained statistically not significant. Moreover, including a squared coefficient for total maternal leave was not significant, indicating a linear effect. The results also remained robust when accounting for maternal employment status after labour market re-entry, fathers’ working hours and household income (Table 2, Model 6). We further tested lagged variables for the duration of leave, which yielded substantively the same results for mothers as those shown in Table 2 (see Online Appendix Table A1 for the full results). Thus, the negative impacts of maternal leave duration on mothers’ relationship satisfaction appeared to last over the longer term. Only the negative impacts of maternal solo leave duration on fathers’ relationship satisfaction were not confirmed by the sensitivity analysis, indicating short-term effects. We estimated an additional model (not shown) controlling for the relative share of leave taken by mothers (mothers’ leave duration divided by the sum of both partners’ leave durations). This model uncovered no significant impact of mothers’ relative leave share, and the negative effect of maternal solo leave length remained significant. In further models (not shown) controlling for formal childcare, the results did not differ substantially. We further tested an interaction effect of relationship duration with the length of maternal and paternal leaves, respectively, and did not find any statistically significant effects suggesting that the effects of leave uptake did not vary by relationship duration.

For the reform evaluation, we applied entropy balancing to create pre- and post-reform groups without significant differences in the means of all control variables (Hainmueller, 2012). As shown in Online Appendix Table A2, the results of the DiM and DiD analyses with entropy balancing did not vary qualitatively from those shown in Table 2. As the reform may also have increased household income among some groups, we also ran the same DiD models without controlling for household income and found unchanged results.

Conclusion

The present study provided new insights into parental leave policies and the role of mothers’ and fathers’ parental leave uptake for relationship satisfaction among parents in a European country with a history of familialist policies and long maternal leaves which has recently undergone a significant policy shift. It extended previous studies by drawing on the strengths of two different methodological approaches and considering possible effects of mothers’ and fathers’ solo and joint leave during children’s early years in greater detail.

We drew on exogenous policy variation resulting from a parental leave reform that provided incentives for fathers to take leave and shorter maternal leaves. Our DiD analyses suggested that mothers who had children after the reform were significantly happier with their relationship. By contrast, fathers’ relationship satisfaction did not seem to be significantly affected by the reform. These results are in line with previous research, which found a positive effect of the reform on parental happiness, with larger effects on maternal wellbeing (Myrskylä and Margolis, 2013). Unlike this latter study, which focused on life satisfaction, we did not find that increases in household income were a mediator of the reform effect on relationship satisfaction.

To investigate potential mechanisms, we explored the individual-level effects of parental leave-taking on relationship satisfaction in a fixed-effects panel model. We found some support for higher relationship satisfaction among fathers and mothers with increasing overall length of paternal leave. This corresponds to previous studies from the US and Korea (Kramer et al., 2019; Petts and Knoester, 2019, 2020), where fathers typically took much shorter leaves of just a few days or a week.

Interestingly, our findings suggest that mothers’ and fathers’ relationship satisfaction declined with increasing duration of maternal solo leave. This finding was remarkably stable and remained significant when lagged variables were used. It corresponds with several studies showing that women are happier with their relationship when they share housework and childcare more equally with their partners (Harris and Morgan, 1991; Kalmijn, 1999; Schober, 2012). Contrary to our assumptions, we found no moderating influence of mothers’ gender ideologies on relationship satisfaction. One possible explanation may be that mothers and fathers with more egalitarian ideals may partly counteract the traditionalisation of the division of domestic work despite long paid leaves by mothers, which offsets the potential negative effects of stronger perceived unfairness. Alternatively, as the data did not allow us to observe couples’ gender ideologies before their first childbirth, our measure might already capture some changes in gender ideologies as a result of experiences of shifts towards a more traditional gender division of labour after previous births. One limitation of our DiD analysis is a lack of relationship quality measures from birth onwards for children born before the 2007 reform. As a result, we analysed medium-term reform effects on parents of 3-year-olds. Our fixed-effects analyses focus on changes in relationship satisfaction in the short to medium term, roughly during a child’s preschool years. Future research is needed to explore which mechanisms drive the relatively strong and consistent effects of maternal leave uptake and whether they fade over time. Ideally, future research should also seek to statistically account for the interdependence of relationship satisfaction of mothers and fathers and their parental leave take-up in couples, for instance, by applying longitudinal structural equation models. Due to sample size restrictions, our analyses were unable to further differentiate between first- and later-born children. The latter may be a more selective sample in terms of satisfaction with the relationship and the gender division of paid and family work. As the reform partly led to different changes in maternal labour market return for mothers with varying household income (Kluve and Tamm, 2013; Kluve and Schmitz, 2018), another promising avenue for future research would be to conduct further subsample analysis by household income or (relative) earnings.

It is important to acknowledge that during the parental leave reform period Germany also expanded the availability and opening hours of childcare facilities. While the increased childcare availability mainly concerned children under 3 years old, we assume that the extension of opening hours affected families with children aged 3–5 years in 2009 and 2010 in similar ways and thus would be controlled for as a time trend in our DiD analysis.

In summary, our findings suggest that both parents’ satisfaction decreases with increasing duration of solo maternal leave. Remarkably, the two analyses in combination seem to suggest that the significant and sizeable positive effect of the parental leave reform in 2007 on German mothers’ relationship satisfaction may have been driven more by the reduction in mothers’ solo leave duration than the increase in fathers’ leave. This is noteworthy given that the latter has received much more attention by scholars and policymakers alike. This finding is plausible, however, as most mothers in Germany tend to take about a year of paid leave, whereas fathers who take leave tend to take 2 months at most. In line with gender revolution theory, our findings provide further evidence that parental leave policies supporting greater gender equality may positively impact relationship quality. This is highly relevant for policymakers in Germany and other EU countries, which are likely to implement similar parental leave measures as a result of the EU Work–Life Balance Directive.

Supplemental Material

sj-pdf-1-esp-10.1177_09589287211056187 – Supplemental Material for Shared leave, happier parent couples? Parental leave and relationship satisfaction in Germany

Supplemental Material, sj-pdf-1-esp-10.1177_09589287211056187 for Shared leave, happier parent couples? Parental leave and relationship satisfaction in Germany by Kristina Goldacker, Janna Wilhelm, Susanne Wirag, Pia Dahl, Tanja Riotte and Pia S Schober in Journal of European Social Policy

Footnotes

Acknowledgements

The authors wish to thank Herman van de Werfhorst for giving valuable feedback to previous versions of the article. This paper uses data from the German Family Panel pairfam, coordinated by Josef Brüderl, Sonja Drobnič, Karsten Hank, Bernhard Nauck, Franz Neyer, and Sabine Walper. Pairfam is funded by the German Research Foundation (DFG) as a long-term project."

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Pia S Schober

Supplemental material

Supplemental material for this article is available online.

References

BMFSFJ (2008) Dossier Elterngeld Als Teil Nachhaltiger Familienpolitik. https://www.bmfsfj.de/blob/93558/1b25367fafda680bbc52a80f3dd240bf/dossier-elterngeld-data.pdf

Broderick

(1993) Understanding Family Process: Basics of Family Systems Theory. Thousand Oaks, CA: Sage Publications.

Brown

(1999) Bowen family systems theory and practice: illustration and critique. Australian and New Zealand Journal of Family Therapy 20(2): 94–103.

Brüderl

Drobnič

Hank

et al. (2017) The German Family Panel (Pairfam). Cologne: GESIS Data Archive. ZA5678 Data file Version 8.0.0.

Bünning

(2015) What happens after the ‘daddy months’? Fathers’ involvement in paid work, childcare, and housework after taking parental leave in Germany. European Sociological Review 31(6): 738–748.

Carlson

Hanson

Fitzroy

(2016) The division of child care, sexual intimacy, and relationship quality in couples. Gender and Society 30(3): 442–466.

Carlson

Pilkauskas

McLanahan

, et al. (2011) Couples as partners and parents over children’s early years. Journal of Marriage and Family 73(2): 317–334.

Chalmers

Meyer

(1996) What men say about pregnancy, birth, and parenthood. Journal of Psychosomatic Obstetrics and Gynecology 17(1): 47–52.

Cooke

(2004) The gendered division of labor and family outcomes in Germany. Journal of Marriage and the Family 66(5): 1246–1259.

10.

Craig

(2006) Does father care mean fathers share? A comparison of how mothers and fathers in intact families spend time with children. Gender and Society 20(2): 259–281.

11.

Dew

Wilcox

(2011) If momma ain’t happy: explaining declines in marital satisfaction among new mothers. Journal of Marriage and Family 73(1): 1–12.

12.

Esping-Andersen

Billari

(2015) Re-theorizing family demographics. Population and Development Review 41(1): 1–31.

13.

Glass

Simon

Andersson

(2016) Parenthood and happiness: effects of work–family reconciliation policies in 22 OECD countries. American Journal of Sociology 122(3): 886–929.

14.

Goldscheider

Bernhardt

Lappegård

(2015) The gender revolution: a framework for understanding changing family and demographic behavior. Population and Development Review 41 (2): 207–239.

15.

Goode

(1960) A theory of role strain. American Sociological Review 25(4): 483–496.

16.

Haas

Hwang

(2008) The impact of taking parental leave on fathers’ participation in childcare and relationships with children: lessons from Sweden. Community, Work, and Family 11(1): 85–104.

17.

Hainmueller

(2012) Entropy balancing for causal effects: a multivariate reweighting method to produce balanced samples in observational studies. Political Analysis 20(1): 25–46.

18.

Harris

Morgan

(1991) Fathers, sons, and daughters: differential paternal involvement in parenting. Journal of Marriage and the Family 53(3): 531–544.

19.

Hecht

(2001) Role conflict and role overload: different concepts, different consequences. Sociological Inquiry 71(1): 111–121.

20.

Henwood

Procter

(2003) The “Good Father”: reading men’s accounts of paternal involvement during the transition to first-time fatherhood. British Journal of Social Psychology 42(3): 337–355.

21.

Hook

(2006) Care in context: men’s unpaid work in 20 countries, 1965–2003. American Sociological Review 71: 639–660.

22.

Hook

(2015) Incorporating “class” into work–family arrangements: insights from and for three worlds. Journal of European Social Policy 25(1): 14–31.

23.

Huebener

Müller

Spieß

, et al. (2016) The parental leave benefit: a key family policy measure, one decade later. DIW Economic Bulletin 6(49): 571–578.

24.

Kalmijn

(1999) Father involvement in childrearing and the perceived stability of marriage. Journal of Marriage and the Family 61(2): 409–421.

25.

Kluve

Schmitz

(2018) Back to work: parental benefits and mother’s labor market outcomes in the medium run. ILR Review 71(1): 143–173.

26.

Kluve

Tamm

(2013) Parental leave regulations, mothers’ labor forces attachment and fathers’ childcare involvement: evidence from a natural experiment. Journal of Population Economics 26(3): 983–1005.

27.

Knight

Brinton

(2017) One egalitarianism or several? Two decades of gender-role attitude change in Europe. American Journal of Sociology 122(5): 1485–1532.

28.

Koslowski

Blum

Dobrotic

, et al. (2019) International review of leave policies and research 2019. https://www.leavenetwork.org/annual-review-reports/

29.

Kotsadam

Finseraas

(2011) The state intervenes in the battle of the sexes: causal effects of paternity leave. Social Science Research 40 (6): 1611–1622.

30.

Kramer

Bae

Huh

, et al. (2019) The Positive spillover and crossover of paternity leave use: a dyadic longitudinal analysis. Journal of Vocational Behavior 115: 1–18.

31.

Laurenceau

Barrett

Rovine

(2005) The interpersonal process model of intimacy in marriage: a daily-diary and multilevel modeling approach. Journal of Family Psychology 19(2): 314–323.

32.

Leitner

(2003) Varieties of familialism: the caring function of the family in comparative perspective. European Societies 5(4): 353–375.

33.

Myrskylä

Margolis

(2013) Parental Benefits Improve Parental Well-Being: Evidence from a 2007 Policy Change in Germany. Working Paper no. 2013-010, 30 August. Rostock, Germany: Max Planck Institute for Demographic Research.

34.

Patnaik

(2019) Reserving time for daddy: the consequences of fathers’ quotas. Journal of Labor Economics 37(4): 1009–1059.

35.

Pettit

Hook

(2005) The structure of women’s employment in comparative perspective. Social Forces 84(2): 779–801.

36.

Petts

Knoester

(2019) Paternity leave and parental relationships: variations by gender and mothers’ work statuses. Journal of Marriage and Family 81(2): 468–486.

37.

Petts

Knoester

(2020) Are parental relationships improved if fathers take time off of work after the birth of a child? Social Forces 98(3): 1223–1256.

38.

Pfahl

Reuyß

(2009) Das neue Elterngeld: Erfahrungen und betriebliche Nutzungsbedingungen von Vätern. Düsseldorf, Germany: Edition der Hans-Böckler-Stiftung.

39.

Pronzato

(2009) Return to work after childbirth: does parental leave matter in Europe? Review of Economics of the Household 7(4): 341–360.

40.

Ray

Gornick

Schmitt

(2010) Who cares? Assessing generosity and gender equality in parental leave policy designs in 21 countries. Journal of European Social Policy 20(3): 196–216.

41.

Rehel

(2014) When dad stays home too: paternity leave, gender, and parenting. Gender and Society 28(1): 110–132.

42.

Schober

(2012) Paternal child care and relationship quality: a longitudinal analysis of reciprocal associations. Journal of Marriage and Family 74(2): 281–296.

43.

Schober

(2014) Parental leave, maternal and paternal domestic work: a longitudinal study of two reforms in West Germany. Journal of Social Policy 43(2): 351–372.

44.

Schober

Zoch

(2019) Change in the gender division of domestic work after mothers or fathers took leave: exploring alternative explanations. European Societies 21(1): 158–180.

45.

Stahl

Schober

(2018) Convergence or divergence? educational discrepancies in work–care arrangements of mothers with young children in Germany. Work, Employment and Society 32(4): 629–649.

46.

Statistisches Bundesamt [Federal Statistical Office] (2020) Statistik zum Elterngeld. Beendete Leistungsbezüge für im Jahr 2016 geborene Kinder nach Geschlecht, Erwerbseinkommen vor der Geburt, Bezugsdauer und Ländern. Wiesbaden, Germany: Statistisches Bundesamt.

47.

Trappe

(2013) Väter mit Elterngeldbezug: Nichts als ökonomisches Kalkül? Zeitschrift für Soziologie 42(1): 28–52.

48.

Twenge

Campbell

Foster

(2003) Parenthood and marital satisfaction: a meta-analytic review. Journal of Marriage and Family 65(3): 574–583.

49.

Wrohlich

Berger

Geyer

, et al. (2012) Elterngeld Monitor Endbericht: Forschungsprojekt im Auftrag des Bundesministeriums für Familie, Senioren, Frauen und Jugend. Report no. 61, 19 February, Berlin, Germany: DIW. https://www.econstor.eu/bitstream/10419/61519/1/diwkompakt_2012-061.pdf

50.

Yavorsky

Kamp Dush

Schoppe-Sullivan

(2015) The production of inequality: the gender division of labor across the transition to parenthood. Journal of Marriage and Family 77: 662–679.

51.

Ziefle

Gangl

(2014) Do women respond to changes in family policy? A quasi-experimental study of the duration of mothers’ employment interruptions in Germany. European Sociological Review 30 (5): 562–581.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.14 MB