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 or Cross-Sectional Study?

Sir,

We read with interest the article “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.” written by Madanagobalane and Anandan[1] published in Indian J Dermatol 2012;57:353-7. The results of the study are interesting and are a matter of concern in psoriasis patients, many of whom may have metabolic syndrome irrespective of disease severity. The purpose of my writing this letter is the way they have labeled their study design – a prospective, observational, descriptive, hospital-based case–control study. Study design is “a plan, structure and strategy of investigations conceived so as to obtain answers to research questions and control variance.”[2] These study designs may be classified broadly as observational or experimental.

Observational studies may be further divided into cross-sectional (survey, prevalence studies) or longitudinal studies (case–control [retrospective], cohort [prospective study]).[2] Thus, the above study was an observational study. The observational studies can also be classified as descriptive or analytical study.

Descriptive studies are observational studies which describe the patterns of disease occurrence in relation to variables such as person, place, and time.[2,3] They are often the first step or initial enquiry into a new topic, event, disease, or condition. Descriptive studies can be divided into two roles: Those studies that emphasize features of a new condition and those which describe the health status of communities or populations. Case reports, case-series reports, before-and-after studies, cross-sectional studies, and surveillance studies deal with individuals. Ecological studies examine populations.

In analytical studies, a hypothesis is tested and an analysis is carried out to ascertain an association between two factors. It can be sub-divided into case–control (retrospective), cohort (prospective), and cross-sectional studies.[2,3]

A case–control study comprises of two groups which are “followed-up” back in time, to determine the proportion in each group that has been associated with the risk factor.[2,3] It is an efficient design for the study of rare diseases and in diseases with long latency periods such as AIDS and cancer. Cohort is not an ideal design for this as the researcher has to follow-up for a long period before the disease manifests.

If the population followed is a defined group of people (a “cohort”), then the study is referred to as a cohort study.[2,3] In a cohort study, the subjects are divided into groups depending on the presence or absence of risk factors and then followed up into the future to find out whether they develop the disease or not.

Cross-sectional (prevalence) study involves the observation of a defined population at a single point in time or time interval.[2,3] Exposure and outcome are determined simultaneously. This means that costs are small and loss to follow-up is not a problem. However, because exposure and outcome are measured at the same time point, the temporal sequence is often impossible to determine. Sometimes, the cross-sectional study can be considered an analytic study, when it is used to test an epidemiological hypothesis. The cross-sectional survey is sometimes referred to as a prevalence study and it can survey or assess the health status of a population. A survey can be defined as a special enquiry which collects planned information from individuals (usually a sample) about their history, habits, knowledge, attitudes, or behavior. It is worth noting that the term “cross-sectional” study is also used in social research. Here, the cross-sectional study refers to a snapshot of a population at a particular point of time.[2,3]

Thus, it is obvious from the above that the design of the study in question was not prospective, but rather cross-sectional. Their title says “prevalence of metabolic syndrome…,” which is a feature of cross-sectional study. To say that it was a case–control study is wrong as it was not a retrospective study.