Abstract
Thriving is a scarcely researched topic in nursing sciences. The present study aimed to explore how older persons experience thriving in care homes as assessed by staff and which demographic characteristics and central interRAI scale factors are associated with thriving. The thriving of 145 residents in four public care homes was measured using the short-form Thriving of Older People Assessment Scale (TOPAS). Both enrolled and registered nurses participated in this study. The data were collected in October to November 2022. Descriptive statistics and logistic regression analyses were performed. Resident thriving was assessed by staff as high. The interRAI scale factor of social engagement showed the strongest association with thriving, followed by gender (female). More attention should be focused on social engagement for care home residents and on the male residents’ thriving. The manuscript was guided by the STROBE checklist.
Introduction
The World Health Organization (WHO) 1 has defined healthy ageing as a process of developing and maintaining functional capacity that enables the well-being of older persons. High-quality long-term care is essential to provide older persons with the care and support required to maintain functional ability consistent with their basic rights, fundamental freedoms and human dignity. 2 Whether care home residents receive satisfactory and dignified care is a current societal issue. A large proportion of older persons in care homes have poor health with impaired physical and cognitive functioning, and many have dementia.3,4 To ensure high-quality care and a good life for older persons, there is a need to explore factors that can affect residents’ experiences of thriving in care homes. 5
Thriving has been defined as a holistic experience of place-related well-being as a result of human-environment interaction.6,7 Bergland et al.8,9 developed the Thriving of Older People Assessment Scale (TOPAS), containing 32 items, designed to measure thriving among care home residents. The short-form TOPAS scale was developed by Baxter et al., 10 based on the theoretical foundations by Bergland and Kirkevold.6,7 The current state of knowledge within thriving research was recently reviewed by Silvennoinen et al., 11 yet research specifically focusing on thriving in care homes is scarce. However, thriving could be central to achieving high-quality care and a meaningful daily life for care home residents. The present study reports how older persons experience thriving in care homes, as assessed by staff using the short-form TOPAS, and which demographic factors and central Resident Assessment Instrument (RAI) scales are associated with thriving.
Background
Good nursing care is based on taking care of patients’ basic needs, such as security, respect for self-determination, dignity, protection of health and life, alleviation of suffering and promotion of a good death. 12 When older persons first move into a care home, obtaining their life history and preferences is necessary to ensure that care can be personalized. 13 It is important to develop knowledge regarding how vitality and lifestyle can be supported when a person becomes dependent on care, to confirm human dignity, as well as to provide meaning, joy and hope in life, despite ill-health and suffering. 14 Loneliness is a common health problem and a risk factor of ill-health among older persons.15,16
The interRAI system (https://interrai.org) was developed for individual care planning, monitoring quality of care, evaluating costs, and developing a payment system for different levels of service structure. The assessment system comprises a wide-ranging standardized mapping of an individual's resources and needs for an individual treatment plan. 17 The interRAI has been developed for several healthcare sectors, including long-term care. It has been translated into many languages in over 35 countries. 18 Each setting-specific interRAI instrument contains a series of questions called a Minimum Data Set (i.e., MDS), a user manual, and a tool for building an individual treatment and service plan to translate the resident's care plan into daily practice.17,19,20 The interRAI is useful for international comparisons, given its good reliability and validity based on user experiences in many countries, and for scientific research on aged care. The interRAI gives staff direction for care planning and provides administrators with a basis to allocate resources and to monitor the quality and results of care.17,19,20 The Finnish Elderly Care Act was recently updated with the rationale of guaranteeing resources for direct resident work and improvement in care quality, and, since April 2023, the RAI has been included in it. 21
Thriving is an under-researched concept in nursing science compared with quality of life (QoL), which is more established. QoL appears to have a more general focus on well-being, 9 while thriving involves well-being in relation to the environment6–8,22,23 and the lifeworld.7,24,25 Thriving as described by Bergland and Kirkevold 7 has seven dimensions, two core dimensions and five additional dimensions. The additional dimensions were not considered to contribute to thriving if the core dimensions were not present. The core dimensions suggested are “the resident's attitude towards living in the nursing home” and “the quality of care and caregivers”, and the five additional dimensions “positive relationships with other residents”, “participation in meaningful activities”, “opportunities to get outside and around”, “relationships with family” and “qualities of the physical environment”. 7 Previous research has shown a positive association between thriving and higher capacity in daily activities, higher cognitive functioning and involvement in everyday activities. 26 Neuropsychiatric symptoms, such as aggression and depressive symptoms, have been shown to be negatively associated with residents’ thriving regardless of their cognitive functioning.26–28 The psychosocial atmosphere in the nursing home also has an impact on thriving.7,22,23,28 Residents describe thriving in their earlier life as being different from thriving in the nursing home. 9 Their wishes, expectations and capacity to interact with peer residents vary, and so does the significance of peer relationships for thriving. 29 Staff can improve thriving by arranging meaningful social and other activities for the residents.7,29 Palmer et al. 30 suggested that professional healthcare for older persons would benefit from a lifeworld-led caring science approach, including readiness for caring dialogue on existential issues.
Aims
The aim of the present study was to explore how older persons experience thriving in care homes as assessed by staff and which demographic characteristics and central RAI scale factors are associated with thriving.
Methods
The study used a cross-sectional design. The manuscript reporting was guided by the STROBE checklist guidelines.
Setting
Data were collected in October to November 2022 in all four public care homes for older persons in a medium-sized (50,000 inhabitants) Finnish city. In the participating care homes, around-the-clock staff were available 20 and residents with and without dementia lived together. The residents without dementia constituted a minority in all care homes. Around-the-clock service housing means living in a barrier-free and safe care home where care is available regardless of the time of day. Care and service plans are made for the residents, based on their ability to function and their resources. Payments for long-term housing services organized by the municipality are income related. 21 All care homes were built in the 2000s, each with approximately 60 beds (altogether 235 beds), a living room, a kitchen, a dining room and a sauna, as well as single rooms for accommodation and access to patios and balconies. Each resident has a room with a private bathroom.
Aged care services became an issue of national importance in Finland in 2019. Regional administrative agencies received several social care complaints and aged care misreports. One of the researchers (H. F.-S.) audited the quality of care within all four public care homes in this city in 2019–2020. Two years later, all four of those public care homes were invited to participate in the present study. The four care homes have been using the RAI assessment since the beginning of the 2000s.
Sample
In Finland, the minimum staffing level for care personnel in units providing 24-h care for older persons was 0.60 employees per resident at the time of the data collection. 31 The majority of staff in Finnish care homes are enrolled nurses, while registered nurses and care aides make up a small minority. The staff in the participating care homes were either enrolled nurses (n = 36 per care home), care aides (n = 3 per care home) or registered nurses (n = 4–5 per care home), but only enrolled and registered nurses were involved in this study. In all care homes, each resident is appointed a staff contact person who is responsible for that resident, with comprehensive and individual care as the goal.
Data collection
This study was carried out using two instruments, the short-form TOPAS and interRAI Long-Term Care Facilities, version, 9.0. The TOPAS questionnaire also included the following demographic characteristics: age, gender, cohabiting status, native language and length of stay.
Short-form TOPAS
Resident thriving was assessed by staff using the short-form TOPAS. 10 The short-form TOPAS includes 15 tem statements, each scored on a Likert-type scale ranging from 1 (“No, I disagree completely”) to 6 (“Yes, I agree completely”). Hence, the short-form TOPAS score can vary from 15 (lowest level of thriving) to 90 (highest level of thriving). The short-form TOPAS has indicated a high level of internal consistency and strong correlation to the original 32-item scale.8,9 The 32-item TOPAS has demonstrated good correspondence between self- and proxy-based ratings.8,9 The short-form TOPAS has not been validated in the Finnish language/population and needs further testing, but the validated Swedish version was translated into Finnish using a forward and backward translation method. 32
InterRAI assessment
In Finland, care plans in care homes for older persons are expected to be based on information from interRAI assessments and the principles of structured data. The interRAI assessments are usually performed by nursing staff and should be completed for each resident every six months or when the resident's condition changes. 33 The six interRAI scales used in the present study are: (1) the Activities of Daily Living Hierarchy (ADL-H), which assesses functional ability in everyday tasks on a scale of 0–6, where 0 represents completely independent and 6 is completely dependent on daily assistance18,34; (2) the Changes in Health, End-stage disease, and Symptoms and Signs Scale (CHESS), which assesses health stability on a scale of 0–5, where 0 represents extremely stable and 5 is extremely unstable heath18,35; (3) the Cognitive Performance Scale (CPS), which assesses cognitive impairment on a scale of 0–6, where 0 represents normal cognition and 6 is extremely severe cognitive impairment18,36; (4) the Depression Rating Scale (DRS), which assesses depression on a scale of 0–14, where 0–2 represent no depression and 3–14 is probable clinical depression18,37; (5) the Pain Scale (Pain), which assesses pain on a scale of 0–3, where 0 represents no pain and 3 is extreme pain18,38; and (6) the Social Engagement Scale (SES), which assesses social activity on a scale of 0–6, where 0 represents minimal and 6 is maximal social engagement.18,39,40
Data for the TOPAS and the interRAI assessments were collected from the four care homes. The interRAI assessment results were derived from the nationwide interRAI assessment performed in September 2022. After ethics approval was received, management in each care home was contacted by email and invited to participate. Digital information sessions were arranged for the managers and the care staff, who were also provided with written information on the aims and the methods of this study. All residents in the care homes were offered the possibility to participate in the study. All residents had either Finnish or Swedish as their native language. The native language of each resident was used when providing information about the study. Each resident was assessed by the staff member who knew that resident best. The staff were urged to do the proxy assessments from a proxy-resident perspective (i.e., to answer the questions as the residents most probably would have answered themselves). The data collected on each resident included the demographic characteristics age, gender, cohabiting status, native language and length of stay. Data were coded, and the participants were anonymous to the researchers.
Data analysis
Descriptive statistics were used to present the demographic characteristics and the total TOPAS scores. Categorical variables are presented in actual numbers and percentages of items, and continuous variables by means. The sample was divided into higher and lower thriving based on a median split of the TOPAS total scores, a cutoff that was also used by Patomella et al. 26 Differences between those groups were tested using chi-squared tests. Data on the interRAI scale factors were also dichotomized. 3 A logistic regression analysis was performed on a model with the TOPAS scores (high/low) as the dependent variable, and with the demographic characteristics (age groups <81 years, 81–90 years and >90 years, gender, length of stay and cohabiting status) and the dichotomized interRAI scale factors (ADL-H, CHESS, CPS, DRS, Pain and SES) as independent variables. p < 0.05 was considered statitically significant in all analyses. All statistical analyses were performed using the STATA, version 18 (StataCorp).
Ethical considerations
This study followed the ethical requirements of the Finnish National Board on Research Integrity. 41 It was conducted in accordance with the Declaration of Helsinki and approved in September 2022 by the Åbo Akademi University Research Ethics Board (09/15/2022). Research permission was also obtained from the municipality that appointed a contact person for the data collection (2512/2022). The participants received a cover letter giving them information on the study and a notice that participation was voluntary, that they could cancel their participation at any time, that cancellation or participation would not affect their care, and that all collected data would be protected. Informed consent was obtained from participants, or their relatives for the residents with severe cognitive impairment (CPS 3–6). 36 The aim of the study was explained during an informed consent process. Residents who were not able to give their consent and had an external custodian did not participate in the study. The data were treated confidentially. 41
Results
Characteristics of the sample
In total, 145 completed proxy-ratings from staff were received (response rate 61.2%). The results concerning demographics and the selected interRAI scales, as grouped by the level of thriving, are shown in Tables 1 and 2, respectively. The mean age of the residents was 86 years (range 63–102 years). The residents were divided into three age groups: <81 years (24%), 81–90 years (47%), and >90 years (29%). Those aged >90 years showed a higher level of thriving than the two younger groups (Table 1). Most residents (77%) were female. Female residents showed higher levels of thriving, representing 85% of those whose thriving was rated as high (n = 62). Of the residents whose thriving was rated low, 69% were female (n = 50) and 31% were male (n = 22). The language proportions were almost equal, with Swedish being the native language for 49% of residents. Native language showed no association with the level of thriving. The overall mean value for the length of stay was 28.9 months. For those with high TOPAS, the mean was 28.2 months and, for those with low TOPAS, it was 29.6 months. This difference was not significant. The median score for thriving among the residents was 71 and the mean score was 70 (range 40–90). For those with low TOPAS, the mean and the median were 61 and 62, respectively. For those with high TOPAS, the mean and the median were 79 and 77, respectively. Of the residents, 85% had an ADL impairment (ADL-H >1), 21% had unstable health (CHESS >2), 84% had dementia-level cognitive impairment (CPS >2), 27% had possible depression (DRS >2), 29% had some form of pain (Pain >1) and 51% had one or more type of social engagement (SES >1) (Figure 1 and Table 2).
Demographic characteristics and proportions of high versus low TOPAS scores.
Abbreviation: TOPAS = Thriving of Older People Assessment Scale.
The sample was divided into high and low thriving based on a median (71) split of the TOPAS total scores. The p-values indicate significance of differences between residents with high and low thriving.
Dichotomized central interRAI scales and proportions of high versus low TOPAS scores.
Abbreviations: ADL-H = Activities of Daily Living Hierarchy; CHESS = Changes in Health, End-stage disease, and Symptoms and Signs Scale; CPS = Cognitive Performance Scale; DRS = Depression Rating Scale; SES = Social Engagement Scale; RAI = Resident Assessment Instrument; TOPAS = Thriving of Older People Assessment Scale.
ADL-H >1: any ADL impairment, CHESS >2: unstable health, CPS >2: dementia-level cognitive impairment, DRS >2: possible depression, Pain >1: any pain, SES >1: one or more types of social engagement. The p-values indicate significance of differences between residents with high and low thriving.
Staff gave the highest TOPAS item-level mean score (5.4) for Q4 “I receive help that is adjusted to my needs” and the lowest item-level mean score (3.6) for Q13 “I am given possibilities to get out and visit places that are important for me”. TOPAS item-level mean scores of >5 were obtained for questions that concerned the quality of the care work and possibilities to keep in contact with relatives/friends. TOPAS item-level mean scores of 4–5 were obtained for questions that concerned how residents experienced living in the care homes, whether they had the opportunity to come out when they wished and to decide how things are placed in their rooms. The lowest TOPAS item-level mean scores of <4 concerned questions on activities.
Associations between TOPAS scores and interRAI scale factors
The results of the logistic regression model showed that, of all the interRAI scales, only SES showed a significant association with thriving (significant at the 5% level) (Table 3). In that model, female gender was also significant at the 10% level.
Factors independently affecting probability of having high TOPAS score.
Abbreviation: SES = Social Engagement Scale.
The results for non-significant variables are not shown.
Discussion
The present study aimed to explore how older persons experience thriving in care homes as assessed by staff and which demographic characteristics and central interRAI scale factors are associated with thriving. The results show that staff rated the residents’ overall thriving as relatively high, which is in line with the study by Baxter et al., 10 who also found staff rated residents as having high TOPAS scores. The results of the logistic regressions showed that the interRAI scale factor SES was significantly associated with higher thriving, indicating that the odds of thriving are 2.4 times greater for older persons with one or more types of social engagement. The odds of thriving were 2.5 times greater for female residents, when controlling for confounders. A control for the female gender was also positive and statistically significant at the 10% level in that model. Morbidity overall was rather low in this study, apart from cognitive impairment (Table 2). Physically ill residents showed a tendency toward higher TOPAS scores and depressed residents toward lower TOPAS scores. In the study by Patomella et al., 26 staff assessed that the residents with less physical and cognitive impairment had a higher level of thriving. The COVID-19 pandemic together with the Finnish restrictions regarding aged care since spring 2020 and the older persons’ perceived loneliness 42 may have had an impact on how staff assessed the residents’ thriving in the present study.
Female residents in this study were rated to have a higher level of thriving than male residents. In the study by Lood et al., 43 some activities in nursing homes were perceived as female activities by male residents, who participated in fewer social activities than female residents. Social and health care often is dominated by women, at both operative and administrative levels and in education, which may have an impact on the activities and operations in care homes that may not always support the thriving of male residents.
The demographic findings concerning higher thriving in relation to advanced age and female gender are in line with previous studies,8,23,26,28,44,45 except for a Chinese study, 46 based on a Chinese version of TOPAS (TOPAS-C), where most residents were male (73.7%). Thriving in the present study seemed to improve with increasing age, although the association was not statistically significant. Another non-significant finding was that status as not cohabiting resulted in higher levels of thriving. Very old residents most often are single or widowed. These residents may have adapted to no longer being able to live at home and try to make the best of their situation in a care home.
The interRAI scale factor SES showed the strongest association with thriving in this study. Social engagement and participation in the institution's life includes making friends, maintaining friendships and participating in group activities. 39 Reduced social engagement may increase loneliness particularly in people with dementia. 47 Drageset and Haugan 15 identified an association between loneliness and nurse-patient interaction and pointed out its importance in alleviating loneliness. In the present study, TOPAS item-level mean scores of >5 were obtained for questions that concerned the quality of the care work and possibilities to keep in contact with relatives/friends (Figure 1). According to Bergland and Kirkevold, 48 interactions between residents and their caregivers depend on residents’ needs and expectations. As articulated by Lämås et al., 49 thriving can be enhanced by offering older persons access to social activities and by supporting them to keep contacts with family and friends. Baxter et al. 25 found that expressions of thriving were recognized by staff through understanding, observing and sensing. Their findings may help staff identify and assess thriving in long-term care and could also be useful for developing staff education and person-centred care. In the study by Bergland and Kirkevold, 7 most residents regarded positive relationships with caregivers and the feeling that caregivers had time to talk to them as extremely important. By organizing pleasant social gatherings, caregivers can have a great impact on developing positive peer interactions and improving thriving. 29 In the study by Patomella et al., 26 positive associations were found between thriving and engagement in varying activities, such as engagement in activity programs, dressing nicely and spending time with someone who the resident likes.

Proportions of each TOPAS item-level score for the 15 TOPAS question items. TOPAS = Thriving of Older People Assessment Scale.
Most residents in this study (85%) were dependent on assistance (ADL-H >1). In the study by Patomella et al., 26 residents who were less dependent in their ADL had higher levels of thriving. The association between ADL-H with thriving was positive, albeit statistically non-significant, in the present study (i.e., those residents who were more dependent on daily assistance showed higher thriving). One explanation could be the increased contact and interaction with staff for those with ADL-H impairment. Staff may have felt that those in need of more help were feeling safer in care homes, which may have had an impact on how they assessed thriving. Nursing home staff have described that they promote resident thriving through personalized interactions that take the resident's individual capabilities into account when providing care. 50 In the present study, the lowest TOPAS item-level mean scores of <4 concerned questions on activities. This finding, rated relatively lower than other items, may indicate a wish for more activities, which is in line with previous studies.7,23,44,45 However, even the lowest scores were above the TOPAS score mean of 3.5. When activities are arranged, the individual needs of each resident should be observed. 44 During the data collection in the present study, several units in the participating care homes had COVID-19 cases and had to limit their operations, including social activities, that may have affected thriving and how staff rated their capacity to meet the residents’ needs.
Most residents (84%) had cognitive impairment (CPS >2). People with dementia in care homes may be able to communicate their needs, and the activities should be planned to correspond to their abilities and interests. 13 Among institutionalized older persons, physical activity and social engagement may slow age-related cognitive decline and dementia onset and decrease mortality rates. 51 According to Patomella et al., 26 thriving is associated with decreased psychological and behavioural problems. Baxter et al. 27 showed associations between thriving, cognitive functioning and neuropsychiatric symptoms, while, in this study, CPS as dichotomized at the level of 3 was statistically non-significant. In the study by Björk et al., 28 the lower the cognitive functioning was, the fewer factors were associated with thriving.
CHESS and Pain did not show significant associations with thriving. The proportions of residents with CHESS >2 and Pain >1 were low, at 21% and 29%, respectively. CHESS has a strong association with mortality in care homes. 35 Pain is a major problem in care home populations,38,52 and is associated with a negative effect on the mood. The audit preceding the present study and training thereafter of nursing staff on pain treatment may have lowered the pain levels in the participating care homes. The association of DRS with thriving was negative but statistically non-significant. Depression might impair the level of thriving, but only 27% of residents showed DRS >2. Since statistical association does not mean causal inference, the cause-and-effect relationship could also be reversed: residents might have been depressed because they were not thriving. Depression is common but underdiagnosed in nursing home residents. 37 Identifying nursing strategies to prevent and reduce depression and anxiety would probably be of great importance for the thriving of care home residents. According to Björk et al., 28 impaired thriving may be indicated by aggression and depressive symptoms. More focus on alleviating these symptoms could improve thriving in nursing homes.
Moving to a care home means starting a new life in a new home, meeting new people, and living a new life without family and with a reduced number of contacts. 16 In the present study, TOPAS item-level mean scores of 4–5 were obtained for questions that concerned how residents experienced living in the care home, whether they had the opportunity to come out when they wished and to decide on how things are placed in their room. All four care homes were relatively newly built and offered good opportunities to either go out into the garden or sit out on large furnished balconies. According to Morris et al., 53 there is a strong relationship between QoL and services and the “home like feeling” that the residents have in the care home. Opportunities to go outside for varying periods contribute to thriving. 7 The COVID-19 pandemic restricted visits outside the care homes during the data collection. In the study by Björk et al., 5 thriving was associated with several environmental factors, with a positive psychosocial climate showing the strongest association. To improve resident thriving in care homes, it is important for decision-makers, managers and staff to address the factors that contribute to thriving and observe thriving in their decision-making, especially for male residents and residents with dementia. Attention should be directed towards staff education, development of working methods and interventions that can improve thriving. If opportunities to enhance thriving are observed, costs in aged care could be reduced by encouraging investments in preventive care.
Methodological considerations
The care homes participating in this study represent the care homes of medium-sized cities in Finland. This study is limited by a small sample size, and further studies with larger and more heterogenous care home samples are needed, preferably with a larger geographical coverage. The sample and results are representative of the situation in a middle-sized Finnish city in the middle of the COVID-19 pandemic, which limits the generalizability of the results.
To ensure that each assessment was based on the best possible knowledge of the resident, the staff member who knew that resident best performed the assessment. 54 The use of proxies is not unproblematic. 45 However, it may be the only way to include residents with severely impaired cognitive functioning in research studies. 45 In this study, the use of proxies was justified as 84% of the residents were rated as having dementia-level cognitive impairment.
During the data collection, the participating care homes were affected by the COVID-19 pandemic, which probably had an impact on the response rate (61.2%). The response time was rather short because we aimed at scheduling the TOPAS assessment as close to the nationwide interRAI assessment as possible. The TOPAS has been shown to be a valid proxy instrument, as evidenced by good reliability between resident and staff ratings.8,9 The short-form TOPAS requires validation in other cultures, languages and care contexts. It has not been validated in the Finnish language and needs further testing.
Definitions for high/low thriving scores have not been established in the literature, but the TOPAS median split score that was used to distinguish higher and lower thriving was also used by Patomella et al. 26 Our study contributes to understanding what higher and lower thriving mean for residents in this context. The dichotomization of the central interRAI scales, as performed in this study according to OECD, 3 may explain some of the differences between the present results and those obtained in earlier studies.
Conclusions
To our knowledge, the present study is the first to evaluate thriving of older persons in care homes as associated with interRAI scales. Significant associations were found between thriving and social engagement with an odds ratio of 2.4, and, at the significance level of 10%, between thriving and female gender with an odds ratio of 2.5. A major goal for care homes worldwide is to guarantee high-quality care for residents and to make life as meaningful as possible, despite multimorbidity, frailty and functional dependence. 45 More attention should be focused on social engagement for the residents in care homes and on the male residents’ thriving. Knowledge concerning factors that are associated with thriving could help staff identify residents at risk of lower thriving and activate all residents in person-centred ways.
Further research is needed on thriving and individualized care, particularly for persons with dementia. In future studies, it could also be interesting to examine how the central interRAI scales are associated with individual TOPAS items to obtain more detailed information regarding possibilities to improve older persons’ thriving. Other interRAI scales, such as the Deafblind Severity Index (DbSI) or the Communication Scale (COMM), could also be relevant parameters to assess in relation to thriving in care homes. Because SES was the interRAI scale factor that showed the strongest association with thriving, research should focus especially on efforts to improve thriving for those residents whose possibilities for social engagement are limited.
Footnotes
Acknowledgements
We wish to thank all the care home residents, relatives, care staff and managers in the participating care homes. Marja Lahti-Elers is specially thanked for her assistance in collecting the data. We also thank interRAI for the interRAI instruments.
Author contributions
All authors contributed to the study design. A-SS was responsible for the data collection. EJ was responsible for the data analysis. All authors have agreed on the final version of the manuscript submitted for publication and meet at least one of the following criteria, as recommended by the ICMJE ( - substantial contributions to the conception and design, acquisition of data, or analysis and interpretation of data, - drafting the article or revising it critically for important intellectual content.
:
Professor Edvard Johansson is a statistician and a member of the author team.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by a grant from the Marianne Armfelt Foundation.
Appendix 1. STROBE checklist.
STROBE Statement: checklist of items that should be included in reports of cross-sectional studies.
