Could you give me an example of mediation related to program evaluation?

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thanks a lot!

For example, we want to evaluate whether providing free lunch to primary students helps them grow taller. The intervention/independent variable is whether accepting free lunches, the short-term incomes are the quantities of nutrients the students consume per day, and the long-term outcome is students’ height. We can understand the mechanisms between these variables including 1) whether providing free lunch increases nutrient consumption; 2) whether the increase in the nutrient consumption is associated with students’ height, 3) whether providing free lunch has direct effect on students’ height; and 4) whether providing free lunch has indirect effect on students’ height through nutrient consumption.