Al lows measurement of frequency of effect of causal factors in different groups. May be used to estimate effectiveness of a given causal factor. May require a long time to complete. Not suited to the study of rare diseases or diseases with long latency periods. The study is backward looking -unlike both experimental and prospective designs, which are forward looking.
Retrospective data is more like survey data than like prospective data but usually more accurate.
The superiority of retrospective study over survey lies mainly in the reliability of the information and in the care with which the control group is selected. With care it is possible to control for most variables that might reasonably be thought to bias the data. Study depends on the quality of historical records.