The American Cancer Society recently announced it needed some volunteers for an upcoming prospective study on cancer. How many volunteers does it need? 500,000.
That's a big study. The idea is to find Americans between 30 and 65, with no cancer, and track them for the next 20 years through blood tests and questionnaires. This Reuters story says it matches some similarly sized trials in Europe and Asia. But it makes me wonder: What's the largest cohort ever assembled for a forward looking study? (It's easier to do retrospective studies with big numbers because there's no tracking to do; it's all done through records). Here's a prospective study in India that claims 14 million participants, but it looks like it's all done through vital statistics records. In the UK, Biobank and the EPIC study both claim half a million participants and make claims of "most participants" status.
It reminds me of my favorite clinical study, the legendary Framingham Heart Study, where the National Heart Institute recruited just about the entire town of Framingham, Mass., to participate in a study on heart disease. The study started in 1948 and continues to this day; it's now tracking a third generation of citizens (and is on at least its third generation of researchers). Unprecendented for it's day, Framingham tracked just over 5,000.