An overview of confounding. Part 2: how to identify it and special situations

Citations Over TimeTop 10% of 2018 papers

Abstract

Confounding biases study results when the effect of the exposure on the outcome mixes with the effects of other risk and protective factors for the outcome that are present differentially by exposure status. However, not all differences between the exposed and unexposed group cause confounding. Thus, sources of confounding must be identified before they can be addressed. Confounding is absent in an ideal study where all of the population of interest is exposed in one universe and is unexposed in a parallel universe. In an actual study, an observed unexposed population represents the unobserved parallel universe. Thinking about differences between this substitute population and the unexposed parallel universe helps identify sources of confounding. These differences can then be represented in a diagram that shows how risk and protective factors for the outcome are related to the exposure. Sources of confounding identified in the diagram should be addressed analytically and through study design. However, treating all factors that differ by exposure status as confounders without considering the structure of their relation to the exposure can introduce bias. For example, conditions affected by the exposure are not confounders. There are also special types of confounding, such as time-varying confounding and unfixable confounding. It is important to evaluate carefully whether factors of interest contribute to confounding because bias can be introduced both by ignoring potential confounders and by adjusting for factors that are not confounders. The resulting bias can result in misleading conclusions about the effect of the exposure of interest on the outcome.

Related Papers

• → Dietary Factors and Early-Onset Colorectal Cancer in the United States—an Ecologic Analysis(2022)18 cited
• → Population Profile of the United States(1967)7 cited
• Is the association between birthweight and height attainment independent of the confounding effect of ethnic and socioeconomic factors?(1993)
• An analysis of nuptiality of population in Zhejiang Province.(1986)
• → Hip fractures The effect of early versus delayed surgery on mortality, hospital stay,and complications in elderly patients(2007)