Abstract
In this viewpoint, we draw attention to using happiness in clinical studies as an interesting outcome that is highly relevant to patients with Parkinson’s disease. Quality of life (QoL) is thus far commonly used as main outcome in clinical trials. Happiness is a part of QoL, but also represents a construct on its own. While QoL mainly consists of quality perceptions of different extrinsic aspects of life, such as the environment or performance, happiness entails the intrinsic quality of the subjective enjoyment of life. Around 70% of people rate happiness as the most important thing in life. Happiness can be a difficult construct to measure, but we argue that self-compassion and well-being could serve as reliable indicators for happiness. We expect that happiness as outcome could probe the true value of an intervention for a patient, well beyond what is captured by more traditional outcomes such as motor scores or the general concept of QoL, which better reflect external factors. Because of the apparent importance of happiness to many people, we recommend that this concept is used more widely as outcome measure in future clinical trials.
Quality of Life (QoL) is a commonly used outcome in clinical trials in various fields, including Parkinson’s disease (PD) [1]. According to the World Health Organization (WHO), QoL is defined as “individuals’ perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards, and concerns” [2]. The term QoL refers to both the positive and negative state of a persons’ life [3] and is often equated with happiness or well-being. While QoL metrics are mainly based on motor skills and driven by extrinsic resources, such as income or employment, happiness is primarily a subjective experience that is pursued intrinsically and that comprises views of persons on their life [4]. Happiness is a part of QoL but does represent a separate construct on its own [5]. QoL entails quality in extrinsic aspects of life, such as environment or performance, whereas happiness is about the intrinsic quality of subjective enjoyment of life [5]. When measuring QoL, the extrinsic factors make it unclear whether intrinsic factors really cause feelings of happiness. Happiness is therefore a valuable concept, above and beyond conventional indicators predicting QoL. And as such, happiness could potentially be considered separately and independently of QoL as a measure of a patient’s status, for example, as measured before and after an intervention [6].
Happiness is often measured by the concepts of well-being and self-compassion [7, 8]. Well-being refers to the sense of wellness of an individual [9], while self-compassion is defined as being kind toward oneself in times of failure and challenge [8]. One study suggested that 69% of people rate happiness as the most important thing in life [10]. Happiness was even rated as close to “extraordinarily important and valuable” in 41 countries in a study about subjective well-being and personal perceptions of health [11]. Moreover, the benefits of self-compassion, as an indicator of happiness, are universal despite cultural differences. Levels of self-compassion and its association with well-being were, for example, measured in Taiwan, the United States and Thailand. In all three cultures, greater self-compassion predicted significantly less depression and higher life satisfaction [12].
Because of this apparent importance of happiness to many people, it is remarkable that this concept is not being included as an outcome measure in clinical trials, for example in the field of PD. Currently, the success of clinical trials mostly depends on improvements in motor scores, such as the motor sub-score of the Unified Parkinson Disease Rating Scale. But the value of an intervention cannot always be translated directly into motor improvements, despite obvious personal benefits. Happiness provides a more reliable overview of the patient’s general status, above routinely used parameters. With the complexity that inevitably accompanies a subjective measurement such as happiness, several factors impact its experience and should therefore be considered as well. For example, premorbid personality style and social interactions need to be accommodated when measuring happiness. Also, alongside these influencing factors, we need to realise that happiness is transient and therefore variable in nature [13]. This subjectivity and the many factors influencing happiness make it more difficult to quantify happiness. Qualitative assessments of happiness are therefore valuable in providing specific contextual information, such as the individual nature of positive feelings, as well as the complex interrelationship with factors such as social interaction, creative energy and greater self-worth. As such, qualitative assessments provide valuable complementary information to the quantitative outcome measurements, which can be used to compare effect sizes across interventions in terms of their influence on patients.
For example, a patient who used to love knitting might score high on a QoL scale, despite being unhappy because of the fact that she cannot handle knitting needles anymore. Most questionnaires or scales do not assess such specific motor impairments. Since this patient could still walk (which the questionnaire did ask for), an acceptable score was obtained on a QoL scale, while this patient nevertheless felt miserable for not being able to knit anymore. This example illustrates that patients may score high on a QoL scale but still have a specific and individually debilitating problem that markedly lowers their actual QoL. Alternative approaches are therefore needed that focus more on the subjective feelings of well-being instead of objective parameters (e.g., walking) that are used as an indicator for well-being.
The capability approach may be a useful alternative, where capability refers to a person’s ability to do specific things. This approach emphasizes the importance of taking someone’s capability to function as a starting point, instead of only looking at scores [14]. Measuring happiness fits well with the capability approach and potentially gives information about otherwise hidden benefits of interventions, which are hard to capture with commonly used questionnaires. Unfortunately, in research, happiness has only scarcely been used as an outcome in clinical trials, even though the subjectively experienced benefits can be very informative and, importantly, can be measured reliably. Specifically, the subjective experience of happiness can be measured precisely and objectively with well-being or self-compassion scales. Examples of measurement scales for subjective well-being are the Satisfaction With Life Scale (SWLS) [15], Positive and Negative Affect Schedule (PANAS) [16], and Scale of Positive and Negative Experience (SPANE) [17]. A measurement scale for happiness with self-compassion is the Self-compassion Scale (SCS) [18–20]. The reliability and validity of these scales have been shown in multiple studies [15–17, 19], although the scales have not yet been validated specifically for PD.
In addition, self-compassion can not only be measured reliably, but it is also a trainable skill that can significantly increase life satisfaction while decreasing depression, anxiety, stress, and emotional avoidance [21]. New non-pharmacological therapies that may potentially have a positive effect on happiness, such as mindfulness [22], dance therapy [23, 24], or music therapy [25], are currently being developed and put to the test in clinical studies. Having reliable scales in these studies that can measure the full impact of such new interventions, well beyond motor scores, may be valuable for patients andtimely.
A PubMed search for clinical trials that measured happiness, well-being, or self-compassion in persons with PD only yielded several small studies: none used self-compassion, one used happiness [26], and ten used well-being as an outcome [27–36] (see Table 1 for more information). Well-being and happiness measurements were used as a primary outcome in five [27, 35] out of eleven clinical trials. Moreover, well-being outcomes were often claimed to be measured, while the scores were derived from QoL questionnaires and not from specific well-being questionnaires. Therefore, we did not include these studies in Table 1 (e.g., [37–48]).
Clinical Trials using happiness, self-compassion or well-being
Looking at the studies measuring happiness, we can conclude that happiness or well-being was only included as a primary endpoint in less than half of the studies, and more often, a QoL questionnaire was used to measure well-being. Also, most studies had included only a limited number of participants and used short follow-ups. These considerations emphasise the need for high-quality studies measuring this important construct. Therefore, we argue that happiness, measured as self-compassion or well-being, deserves further exploration in PD research, particularly when considering non-pharmacological therapies, such as dance therapy, music therapy or meditation. To further document the actual benefits of those therapies, happiness may represent a useful and relevant outcome.
CONFLICT OF INTEREST
Prof. Bloem currently serves as Editor-in-Chief for the Journal of Parkinson’s disease, serves on the editorial board of Practical Neurology and Digital Biomarkers, has received honoraria from serving on the scientific advisory board for Zambon, Biogen, UCB and Walk with Path, has received fees for speaking at conferences from AbbVie, Zambon, Roche, GE Healthcare and Bial, and has received research support from the Netherlands Organization for Scientific Research, the Michael J Fox Foundation, UCB, Abbvie, Zambon, the Stichting Parkinson Fonds, the Hersenstichting Nederland, the Parkinson’s Foundation, Verily Life Sciences, Horizon 2020, the Topsector Life Sciences and Health, and the Parkinson Vereniging. Dr. De Vries receives research support from The Netherlands Organization for Health Research and Development and from the Michael J Fox Foundation.
Footnotes
ACKNOWLEDGMENTS
Special thanks to Inge Rabeling-Keus for her help and support during this process.