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LETTERS TO EDITOR  
Year : 2018  |  Volume : 60  |  Issue : 4  |  Page : 514
Selecting controls in a case–control study


Department of Community Medicine, Dr. RPGMC, Tanda, Kangra, Himachal Pradesh, India

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Date of Web Publication28-Nov-2018
 

How to cite this article:
Raina SK. Selecting controls in a case–control study. Indian J Psychiatry 2018;60:514

How to cite this URL:
Raina SK. Selecting controls in a case–control study. Indian J Psychiatry [serial online] 2018 [cited 2018 Dec 17];60:514. Available from: http://www.indianjpsychiatry.org/text.asp?2018/60/4/514/246201




Sir,

Went through with interest article entitled “psychological features in patients with and without irritable bowel syndrome: A case–control study using symptom checklist-90-revised” published in Indian J Psychiatry (2015; 57: 68-72).[1] The authors deserve appreciation for their effort. However, I would like to draw the attention of the authors to two points of concern. One concern the methodology used to conduct this study, and the other is regarding the numbers presented by the authors in their results section.

The authors state that a total of 153 consecutive outpatients (cases) and 163 controls were invited to complete the Symptom Checklist-90-Revised instrument to assess psychological distress. The control group for the study included individuals who were referred to the other clinics due to medical problems rather than gastrointestinal chief complains. The authors have used logistic regression analysis for controlling confounding effect and included demographic variables including age, gender, educational level, marital status, employment status, smoking, alcohol use, and body mass index (BMI) for analysis as covariates. However, it appears that the most important of covariates such as psychological/psychiatric conditions have been ignored. A mention on the psychological/psychiatric health of controls should have found a mention in the “material and methods” section of this study. The selection of good controls is the hallmark of all case–control studies.

It is generally believed that there are four basic principles that govern case–control studies.[2] These include; study base, deconfounding, comparable accuracy, and efficiency. Agreed, it may be difficult or impossible to satisfy all principles in a study and “ideal” control group rarely exists in epidemiologic studies. However, an effort to meet with them is always beneficial.

This takes me to my second concern. A look at [Table 1], titled “demographic characteristics of participants” (reproduced below) reveals a discrepancy in the numbers presented. The IBS patients (cases) under single/married heading do not add up to 153 (50 + 96 = 146). Similarly, for the controls under the same heading, the numbers do not add up to 163 (67 + 94 = 161). A look at cases and controls under heading BMI shows similar discrepancies (cases; 87 + 65 = 152 and controls; 130 + 58 = 158). However, of much concern are the numbers shown for “controls” under the headings “nonsmoker/ever smoked.” The numbers for controls under “nonsmoker/ever smoked” is 263 instead of 163.
Table 1: Demography characteristics of participants

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Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Farbod F, Farzaneh N, Bijan MD, Mehdi G, Nosratollah N. Psychological features in patients with and without irritable bowel syndrome: A case-control study using symptom checklist-90-revised. Indian J Psychiatry 2015;57:68-72.  Back to cited text no. 1
[PUBMED]  [Full text]  
2.
Wacholder S, McLaughlin JK, Silverman DT, Mandel JS. Selection of controls in case-control studies. I. Principles. Am J Epidemiol 1992;135:1019-28.  Back to cited text no. 2
    

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Correspondence Address:
Sunil Kumar Raina
Department of Community Medicine, Dr. RPGMC, Tanda, Kangra, Himachal Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/psychiatry.IndianJPsychiatry_43_15

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    Tables

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