Retrospective studies - utility and caveats.

A thorough understanding of the pros and cons of the various study designs is critical to correct interpretation of their results. Retrospective studies are an important tool to study rare diseases, manifestations and outcomes. Findings of these studies can form the basis on which prospective studies are planned. Retrospective studies however have several limitations owing to their design. Since they depend on review of charts that were originally not designed to collect data for research, some information is bound to be missing. Selection and recall biases also affect the results and reasons for differences in treatment between patients and lost follow ups can often not be ascertained and may lead to bias. Readers need to critically evaluate the methods and carefully interpret the results of retrospective studies before they put them to practice. Researchers should avoid over generalisation of results and be cautious in claiming cause-effect relationship in retrospective studies.