In a mediation analysis, what is the standardized measure of the indirect effect defined as the indirect effect multiplied by the ratio of the standard deviation of the predictor to the standard deviation of the outcome?

• A. Indirect effect
• B. Mediation effect
• C. Index of mediation
• D. Mediator index

Answer: (C)

In mediation analysis, expressing the indirect effect in standardized units lets you compare effects across different scales. The indirect effect (the product a×b) tells you the amount of change in the outcome through the mediator, but it depends on the units of X and Y. By multiplying the indirect effect by the ratio of the predictor’s standard deviation to the outcome’s standard deviation, you convert that mediated impact into standard deviation units. This standardized measure is called the index of mediation. It captures how large the mediated effect is in a unitless, comparable way, making it easier to compare mediation strength across studies or variables with different scales. The plain indirect effect is unstandardized, and terms like mediation effect or mediator index aren’t the standard names for this particular standardized metric.