Authors' reply.

Sir,

We thank you for the query regarding our recent article titled “Prevalence of metabolic syndrome in south Indian patients with psoriasis vulgaris and the relation between disease severity and metabolic syndrome: A hospital-based case–control study.”[1] The authors have stated the definitions of study designs from the “Park's Textbook of Social and Preventive Medicine” and “A Practical Approach to PG Dissertation.”[234] However, in epidemiological studies there are no rigid barriers and the references quoted by the author are only an insight into these terms for easy understanding of beginners.

They have classified longitudinal studies into case–control (retrospective) and cohort (prospective). Such rigid classification systems are not applicable in research practice. A case–control study design is not limited to a retrospective nature as suggested in the query. A case–control study design can be used in a prospective manner (i.e., for following up patients), for example, we can choose to prospectively follow up patients with and without a condition of interest for a period of time, to observe whether the condition under study is being observed.[5]

This paper is part of a long-term prospective study in which patients are still being followed up. The readers might have been misled by the use of the word “prospective” in the study design section. To place things in the right perspective, we would like to add a sentence in the study design section explaining that the results of this article pertain only to the baseline results of the prospective study.

A case–control study is “an observational epidemiological study of persons with the disease of interest and a suitable control group of persons without the disease.” The potential relationship of a suspected risk factor or an attribute to the disease is examined by comparing the diseased and non-diseased subjects with regard to how frequently the factor or attribute is present in each of the groups (diseased and non-diseased).”[5] A case–control study can also determine prevalence (prevalence case–control study), which was the case in our study.[5]

Our title, “Prevalence of metabolic syndrome in south Indian patients with psoriasis vulgaris and the relation between disease severity and metabolic syndrome: A hospital-based case–control study,” means that a cross-sectional survey was performed but this is still a case–control study and our title appropriately reflects the research question, the study design, and the population that was studied.