You probably won't need to ask any more questions. If it's a retrospective study, and the data wasn't validated independently of the survey, you can discard it. Armed with this knowledge, you are now qualified to determine the merit of just about any epidemiological study. You will need to find the original study, of course, not just the news story on it. Fortunately, many of them can be found on the Internet with a bit of digging.
Most studies start with an abstract, a condensed version of the study.
Sometimes the abstract is all you need to spot a bogus study. If the abstract passes the test, read the actual study. At first glance they may seem nearly impossible to decipher, but it gets easier after you've stumbled through a few. You may want to bookmark this page as a reference. More Information BioMedNet gathers information from thousands of medical journals.