However, a large sample size is not a guarantee of accuracy. A poorly done study using huge samples can be as worthless as a study with a tiny sample. Survey Errors Retrospective studies ask respondents to remember things from years ago, then treat those recollections as if they were valid data. If that question pops up in the middle of a survey you're likely to guess, and guess wrong. Your wrong guess will be pooled with many other wrong guesses to create a study that that is pure fiction.
Recall bias makes most retrospective studies worthless.
Some people will intentionally lie on a survey. For instance, some smokers will tell interviewers they don't smoke, especially if they only smoke a few cigarettes a day or if the interviewer exhibits a disapproving attitude. When studying something as rare as lung cancer, even a few errors can skew the study significantly. Unless the data is verified, information gathered from surveys should be considered highly suspect. It is possible to change the outcome of a survey by changing the wording of the questions, or even the order the questions are asked.