Which of the following is a way to reduce confounding in the design stage of a study?

Reducing confounding in the design stage of a study is crucial for ensuring that the results are valid and accurately reflect the relationship between the exposure and the outcome. Matching and restriction to one level of a confounder is an effective method because it involves selecting study participants in such a way that the potential confounding variable is controlled for, either by ensuring that it is the same across groups or by limiting the study to a specific group that shares a similar level of the confounder.

For instance, if age is a confounding factor in a study examining the effects of a drug, researchers can choose to only include participants within a specific age range. This strategy ensures that differences in outcomes are less likely to be influenced by age differences among participants.

This means that any variations in the outcomes can be more confidently attributed to the primary exposure of interest, rather than biases introduced by the confounder. Hence, using matching and restriction effectively mitigates the potential biases that could distort the findings of the study by controlling for the confounding variable right from the design phase.