It is a great pleasure to know that our hard work has fulfilled the general expectations of the AJO-DO readers, and we hope that this opportunity to explain any obscure point can make our study even more useful. We observed that the main concern of this letter focused on the study design classification, since it was assumed that retrospective and longitudinal study features could not coexist in the same research. In fact, several studies with a similar design have been equally classified, and the PubMed electronic database shows 1180 retrieved articles when the key words “retrospective longitudinal” or “longitudinal retrospective” are searched. Thus, longitudinal and retrospective seem to be complementary and not exclusionary concepts because the former indicates that the data of the same sample were (retrospective) or will be (prospectively) sequentially collected through time, whereas the latter represents retrieval of data that have been collected at 1 time point (cross-sectional) or at different times (longitudinal). If there are antagonistic study designs, they would be “cross-sectional vs longitudinal design” or “prospective vs retrospective design,” but not “longitudinal vs retrospective.” Even so, it must be considered that historically controlled studies, for instance, can bring together prospective and retrospective data in the same research without any ideological conflict. Thus, the different methods of study design classification should not be used as a Proscrustes bed, which tries to frame the several kinds of research and their particularities in a rigid framework. In our article, we think that the described study features are not in conflict with each other. However, we consider that Dr Goje was not wrong when he classified our recently published work as a retrospective cohort study because cohort studies can be considered a type of longitudinal observational study of a cohort of patients because of the longitudinal nature of data collection. In fact, the term “cohort” is derived from the Latin word “cohors”—“legion of Roman soldiers”—which has been adopted into epidemiology to define a set of people followed over a period of time. Thus, longitudinal studies may take numerous forms, including retrospective longitudinal studies, which are characterized by collecting data on subjects who were previously longitudinally followed. Therefore, this seems to be more a semantic question than a study design problem to be solved.
Thank you for your interest.