Mental health conditions are usually assessed through conversations, questionnaires and evaluations by trained health professionals. Before their fingertip measurements were taken, participants completed a widely used questionnaire containing 21 questions about symptoms of depression, anxiety and stress. The participants were grouped according to questionnaire answers rather than formal diagnoses made by psychiatrists, psychologists or other mental health professionals. The study also created a dataset containing physical measurements from participants across a broad age range and many countries. If you care about mental health, please read studies about 6 foods you can eat to improve mental health, and B vitamins could help prevent depression and anxiety.