DecodeME has built the largest ever cohort of people with ME/CFS who have created a rich dataset through their participation in both our genetic study and through our extensive questionnaires. This is already helping researchers better understand the different ways ME/CFS affects people, which could inform how participants are selected or grouped in future studies – for example, by onset type, severity, or biological differences. Having a well-defined cohort improves the quality and impact of future research. The DecodeME questionnaires are available publicly[link], and we will make our algorithms for cohort selection available to other researchers on request.