What study would best suit looking at the association between low birthweight and later academic performance? Note - 1000 low birth weight children and 3000 normal birthweight children were included in the study.

(a) Retrospective cohort study
(b) Case-control study
(c) Case series.

I don't think it is a case series, but really having trouble deciding between (a) and (b). I know they are not the same but still keep going back and forth? Any suggestions?


2 Answers 2


The choice depends on how your data were collected or sampled. Specifically, if participants were sampled on the exposure (birthweight), then you are conducting a cohort study; if sampled on the outcome (academic performance) then it's a case-control study. I assume your data were sampled on the exposure since it looks like that the numbers 1000 and 3000 were determined by the investigator.


I agree with @toutou. Here is a nice image for the difference between the two from Observational Studies: Cohort and Case-Control Studies. Plastic and Reconstructive Surgery 126(6):2234-2242, December 2010.

From Plastic and Reconstructive Surgery126(6):2234-2242, December 2010.


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