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.
Keywords: Parkinson’s disease; Quality of Life; complementary therapies; happiness.