Anupam Das1, Aparajita Ghosh1. 1. Department of Dermatology, KPC Medical College and Hospital, Kolkata, West Bengal, India. E-mail: anupamdasdr@gmail.com.
Sir,We have read the correspondence by Kaushal, wherein the author has mentioned that cross-sectional study is a type of descriptive design. Adding to the confusion, the author has stated that cross-sectional studies and analytical studies belong to two different watertight compartments.[1]In this context, we would like to point out some fallacies in the position taken by Kaushal.[1] Actually, observational studies are of two kinds, based on whether there is a control group. If there is none, these are descriptive studies. If there is one, it is an analytical study. Based upon whether the participants are included on the basis of exposure, outcome, or both at the same time, the analytical studies are divided into three types – cohort (participants included on the basis of exposure), case–control (participants included based on the outcome of interest), or cross-sectional (where the exposure and outcome are assessed during the same time point in two groups, the test group and the control group).In a cross-sectional study, the investigator is supposed to measure the outcome and the exposure in the participants at a single point of time. There is no question of follow-up of the participants. In case–control studies, participants are selected on the basis of the outcome status, and in cohort studies, participants are selected based on the exposure status. However, the participants in a cross-sectional study are just selected based on the inclusion and exclusion criteria set for the study. Once the participants have been selected for the study, the investigator follows the study to assess the exposure and the outcomes.[2]It is unfortunate that the correspondent has jumbled up the methodologies of research in epidemiological studies.[1] However, she has correctly pointed out that a cross-sectional study can never be a prospective one, wrongly stated in the study by Hazarika and Archana.[3]The purpose of penning down this correspondence is to highlight the basic concepts of study design, the knowledge of which is mandatory for a prospective author of any journal dealing with clinical research.