Prospective study
Prospective studies are those in which researchers examine a group of people at a certain point in time and then monitor them going forward in time, often for years, to see which members of the group develop certain diseases or conditions. The purpose is usually to find an association between an activity or habit and a later health condition. A good example is the Iowa Women's Health Study, which followed over 28,000 women living in Iowa from 1986 to 1997. It made the surprising finding that drinking caffeinated coffee was associated with a lower than normal risk of developing Type 2 Diabetes. While prospective studies do not generally provide strong proof of cause and effect, they are good at finding unexpected associations, like this one, which may be found to be causal by a future controlled study.