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Considerable research has established a link between ADHD symptoms in childhood and depression later in life. Although this correlation exists, it does not tell us how the two variables are related or why some children with ADHD develop depression and others do not. To answer more complex and interesting questions like these, researchers look for mediators and moderators (Baron & Kenny, 1986).

A mediator is a variable that can help explain how two variables are related. Mediator variables explain the mechanism by which one variable predicts another variable. Mediators tend to be continuous variables—that is, they range from low to high and everywhere in between (Figure 3.3).

Description

Figure 3.3 ■ Mediation and Moderation

Note: Mediators explain how two variables are related. Parenting a child with ADHD can cause stress and conflict in the home; the more stress and conflict, the higher children’s likelihood of depression (Humphreys et al., 2017).

Note: Moderators affect the direction or strength of the relationship between two variables. Children’s likelihood of depression depends on whether they are rejected by peers (Humphreys et al., 2017).

For example, parenting stress may mediate the relationship between ADHD in childhood and depression later in life. Children’s ADHD symptoms can increase parenting stress, prompting parents to lose their temper, blame their children for their inattention or hyperactivity, or discipline their children in harsh or punitive ways. Over time, these problematic parenting behaviors can cause children to feel depressed (Humphreys, Galán, Tottenham, & Lee, 2017).

A moderator is a variable that affects the direction or strength of the relationship between two other variables. Moderator variables help identify the conditions under which one variable predicts another variable. Moderators tend to be categorical variables such as gender (i.e., boy, girl), age (e.g., child, adolescent), ethnicity (e.g., White, non-White), family income (e.g., low income, middle class), and diagnostic status (e.g., ADHD, non-ADHD).

For example, peer rejection may moderate the relationship between ADHD in childhood and depression later in life. Children with ADHD who are rejected by their classmates and who have few friends are at increased risk for depression and other mood problems. In contrast, children with ADHD who are able to make friends and sustain relationships with classmates are less likely to become depressed (Humphreys et al., 2017).

Mediators and moderators are important because they can suggest ways to prevent or to treat childhood problems. For example, one way to prevent depression in children with ADHD is to help their parents manage their stress levels and avoid negative interactions with their children. A second strategy is to help children build friendships and avoid rejection by their classmates (Evans, Owens, Wymbs, & Ray, 2019).

Review

 Correlational studies allow researchers to explore relationships between variables. The correlation coefficient (r) shows the strength and direction of the linear relationship between two variables. A correlation means that the two variables are associated with each other; it does not imply that one variable causes or affects the other.

 Cross-sectional studies examine correlations between variables at the same point in time. Longitudinal studies examine correlations between variables at different points in time.

 Mediators explain how two variables are related. They are usually continuous variables. Moderators explain the conditions under which two variables are related. They are usually categorical variables.