To design a study to assess if smoking and lung cancer is related, which of the following is incorrect?
A. Prospective cohort study = To follow a group of smokers and non-smokers and compare them in future for the onset of lung cancer.
B. Retrospective cohort study = To search the the medical records of 20 years ago of smokers and non-smokers and compare their subsequent onset of lung cancer (also called historical control study).
C. Case-control study = To compare a group of lung cancer individuals (case) with a group of non-lung cancer individuals (controls) and assess which group has more smokers (also called retrospective study)
D. Nested case-control study = case-control study with matching done using statistical methods

Answer: D 

Nested case-control study is a case-control study in which cases and controls are drawn from within a prospective study. It is done in the middle of a prospective cohort study before the whole follow-up period is complete, i.e. it is nested within a prospective cohort study. Nested case-control design thus potentially offers reductions in costs and efforts of data collection and analysis compared with the full cohort approach.

For meaningful comparison using the above methods, the individuals must be alike and differ only by the characteristic of interest, i.e. well-matched. Statistical methods can also be used to control for the differences if matching has not been done.