The difference between Moderation and mediation

Mediation

• Definition: Mediation explains how or why an independent variable (IV) affects a dependent variable (DV) through a third variable, called the mediator (M).
• Purpose: To identify the mechanism or process underlying the relationship between IV and DV.
• Key Question: "Why does $X$ affect $Y$?"

Structure:

• IV ($X$) → Mediator ($M$) → DV ($Y$)
• The effect of $X$ on $Y$ is broken into:
  1. Direct Effect: Effect of $X$ on $Y$ not involving $M$.
  2. Indirect Effect: Effect of $X$ on $Y$ via $M$.

Example:

• Hypothesis: Time Management ($X$) improves Academic Performance ($Y$) by increasing the Effectiveness of ODL ($M$).
• Here, the mediator ($M$) explains how Time Management influences Academic Performance.

Visualization:

X → M → Y

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2. Moderation

• Definition: Moderation explains when or under what conditions the relationship between an independent variable (IV) and a dependent variable (DV) changes, based on a third variable called the moderator (Z).
• Purpose: To assess whether the strength or direction of the relationship between IV and DV depends on $Z$.
• Key Question: "Under what conditions does $X$ affect $Y$?"

Structure:

• IV ($X$) → Moderator ($Z$) modifies the strength/direction of the IV-DV relationship.

Example:

• Hypothesis: The relationship between Time Management ($X$) and Academic Performance ($Y$) is stronger for students with higher Motivation ($Z$).
• Here, the moderator ($Z$) influences when or how strongly Time Management affects Academic Performance.

Visualization:

 X  →  Y
 ↑
 Z



Practical Differences
Statistical Test:
Mediation: Focuses on indirect effects ($a \cdot b$).
Moderation: Focuses on interaction effects ($X \times Z$).
Software:
Mediation: Often analyzed using mediation-specific tools like PROCESS or SEM.
Moderation: Analyzed using interaction terms in regression.