Which statement correctly distinguishes a mediator from a moderator?

Which statement correctly distinguishes a mediator from a moderator?

• A. A mediator explains how or why an effect occurs, while a moderator affects the strength or direction of the effect across levels of another variable.
• B. A mediator is a type of sampling error, while a moderator is a measurement error.
• C. A mediator is used only in qualitative studies; a moderator only in quantitative.
• D. A mediator directly causes the outcome; a moderator is an outcome variable.

Answer: (A)

The main concept tested is how mediators and moderators differ in explaining relationships between variables. A mediator explains how or why an effect occurs by carrying the influence of the independent variable to the dependent variable; it sits on the causal path and helps reveal the mechanism. A moderator changes the strength or direction of that relationship depending on the level of another variable, producing an interaction that means the effect varies across subgroups. For example, stress might lead to illness partly because it reduces immune function—that immune function mediates the stress–illness link. Another variable, like social support, could moderate the link by weakening the association when support is high, so the effect of stress on illness depends on the level of support. This aligns with the correct option, which states the mediator explains how or why an effect occurs, while a moderator affects the strength or direction of the effect across levels of another variable. The other statements mischaracterize these roles—for instance, treating a mediator as a sampling or measurement error, or claiming mediators are only for qualitative studies, or confusing the roles with outcomes.

The main concept tested is how mediators and moderators differ in explaining relationships between variables. A mediator explains how or why an effect occurs by carrying the influence of the independent variable to the dependent variable; it sits on the causal path and helps reveal the mechanism. A moderator changes the strength or direction of that relationship depending on the level of another variable, producing an interaction that means the effect varies across subgroups.

For example, stress might lead to illness partly because it reduces immune function—that immune function mediates the stress–illness link. Another variable, like social support, could moderate the link by weakening the association when support is high, so the effect of stress on illness depends on the level of support.

This aligns with the correct option, which states the mediator explains how or why an effect occurs, while a moderator affects the strength or direction of the effect across levels of another variable. The other statements mischaracterize these roles—for instance, treating a mediator as a sampling or measurement error, or claiming mediators are only for qualitative studies, or confusing the roles with outcomes.