Article Prospective case-control study of premenopausal serum estrad...

This study could have been analysed as a cohort study, comparing breast cancer incidence between initial low and high hormone levels. then it would be called a prospective study.

However because of the many "exposure" variables and confounders, it has been analysed as a case referent study within the cohort, using all incident cases.

The"exposures" of cases and non cases referents are compared. In this sense.it is retrospective as you are working back from the accumulated cases and comparing their exposures with those of the referents.

That makes sense! Very helpful feedback

Hi Melvin,

The main difference between case-control and cohort studies is the method of participant selection. In case-control studies subjects are selected based on the presence or absence of an outcome while in cohort studies selection is based on the presence or absence of an exposure.

While the direction of enquiry is often a defining characteristic between the two studies, I'd be of the opinion that this should not be the case. It may just be possible to have a 'prospective case-control study' if one is interested in exploring secondary outcomes from a group selected based on a primary outcome.

Regards,

Case-control studies are in general retrospective, and the cohort studies are in general prospective and many references use these term as synonyms. What I have read many years ago in the book 'epidemiology in Medicine', the case-control studies can be prospective if you start collection of the cases and controls after the start of the study. It is retrospective in case you search the files of the patients who had been admitted (or treated on ambulatory bases) before the start of the study.

Thanks all for good and interesting answers and contributions.

I have also learnt that the case control study can be prospective but the initial study is usually cohort; thereafter every one who will get the disease or outcome of interest will be a case and any one who will not get that disease or outcome of interest will be treated as a control. These kind of studies are also termed as nested case-control studies i.e. the case-control study is nested within cohort study and hence will be conducted prospectively.

The nested case-control studies are good in studying diseases that have not yet been well studied because researchers sometimes find surprising results in such situations.

Dear Dr. Melvin George,

According to J. Last's "A Dictionary of Epidemiology" (4th ed., p. 22), "cases and controls in a case control study may be accumulated "prospectively," that is, as each new case is diagnosed it is entered in the study. Nevertheless, such a study may still be called "retrospective" because it looks back from the outcome to its causes".

Best regards!

Some scholars suggest that case control studies conducted inside the big cohort (i.e. nested case control study), can be taken as prospective type of case control studies; otherwise in most of the time it is retrospective type, since the studies begin after the occurrence of the outcome. [the base to say either retrospective or prospective is the time sequence between the beginning of the study and occurrence of the outcome. For prospective type------study begins before the occurrence of the outcome and the reverse is true for retrospective type.]

Since the outcome is already known and study begins with it, it should be called a retrospective study only.

yes, it could be prospective, and retrospective as well,