Given the media attention devoted to weak observational claims about health (miracle vegetables, chemophobia of the month) and the rampant mistrust of science that has resulted, it is worth asking if they're worth the expense at all.
The answer is that they probably are, though only for smaller programs.
If you are not familiar with the term, an observational study is just what it sounds like; in contrast to an experiment, which is what most people think of as science, an observational study instead observes a population to see what they have in common, such as the impact of various lifestyle and environmental factors on diseases. There are two types of observational studies: case-control and cohort. In my short primer ...