Types of bias in case control studies

Case-control and Cohort studies:

Types of bias in case control studies

Abstract Observational studies are an important category of study designs. To address some investigative questions in plastic surgery, randomized controlled trials are not always indicated or ethical to conduct.


Instead, observational studies may be the next best method to address these types of questions. Well-designed observational studies have been shown to provide results similar to randomized controlled trials, challenging the belief that observational studies are second-rate.

Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures.

In this review article, we describe these study designs, methodological issues, and provide examples from the plastic surgery literature. However, RCT methodology, which was first developed for drug trials, can be difficult to conduct for surgical investigations.

Results from observational studies are often criticized for being vulnerable to influences by unpredictable confounding factors. However, recent work has challenged this notion, showing comparable results between observational studies and RCTs.

Observational studies fall under the category of analytic study designs and are further sub-classified as observational or experimental study designs Figure 1. The goal of analytic studies is to identify and evaluate causes or risk factors of diseases or health-related events.

The differentiating characteristic between observational and experimental study designs is that in the latter, the presence or absence of undergoing an intervention defines the groups.

Case-control and cohort studies offer specific advantages by measuring disease occurrence and its association with an exposure by offering a temporal dimension i. Cross-sectional studies, also known as prevalence studies, examine the data on disease and exposure at one particular time point Figure 2.

In this review, we will primarily discuss cohort and case-control study designs and related methodologic issues.This statement is applicable to cohort studies, case-control studies, and cross-sectional studies.

In fact, 18 of the checklist items are common to all three types of observational studies, and 4 items are specific to each of the 3 specific study designs. We discuss two classes of bias that arise in case–control studies, selection bias and information bias.

A third source of bias, confounding, is not considered in this article. Mainly results from procedures used to select subjects into a study.

Types of bias in case control studies

In a Case-Control selection bias is when selection/participation of cases and controls is related to EXPOSURE status.

In a Cohort study selection bias is when selection/participation of the exposed and .

Self-Selection Bias

Breslow N. Design and analysis of case-control studies. Annu Rev Public Health. ; – Greenland S, Thomas DC.

Observational Studies: Cohort and Case-Control Studies

On the need for the rare disease assumption in case-control studies. Am J Epidemiol. Sep; (3)– Greenland S.

Types of bias in case control studies

Control-initiated case-control studies. Int J Epidemiol. Mar; 14 (1)– Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence. These types of studies, along with randomised controlled trials, constitute analytical studies, whereas case reports and case series define descriptive studies (1).

Confounding and Bias in Case-Control Studies Ching-Lan Cheng (鄭靜蘭), Ph.D. Assistant Professor Institute of Clinical Pharmacy and Pharmaceutical Sciences, • Distinguish two basic types of information bias – Non-differential-Misclassification between groups is approximately equal.

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