Fit a multiple regression model, testing whether a mediating variable partly or completely mediates the effect of an initial causal variable on an outcome variable. Think about whether or not the model will meet assumptions.
Fit the model, testing for mediation between two key variables.
Analyze the output, determining whether mediation was significant and how to interpret that result.
Reflect on possible implications of social change.
Hypothetical Scenario:
We’ll examine the relationship between:
- Causal Variable (X): Socioeconomic Status (SES)
- Mediating Variable (M): Access to Healthcare
- Outcome Variable (Y): Overall Health Outcomes
We hypothesize that SES (X) influences access to healthcare (M), which in turn influences overall health outcomes (Y). We want to test if access to healthcare mediates the relationship between SES and health outcomes.
1. Assumptions of Multiple Regression:
Before fitting the model, we must consider the assumptions of multiple regression:
- Linearity: The relationships between variables are linear.
- Independence of Errors: The errors (residuals) are independent.
- Homoscedasticity: The variance of errors is constant across levels of the predictor variables.
- Normality of Errors: The errors are normally distributed.
- No Multicollinearity: Predictor variables are not highly correlated.
We would need to check these assumptions using diagnostic plots and statistical tests (e.g., scatterplots, residual plots, VIF) after fitting the model.
2. Fitting the Mediation Model:
We will use a series of regression models to test for mediation, typically following Baron and Kenny’s (1986) approach, or a more robust approach such as bootstrapping.
- Model 1: Total Effect (X on Y):
Y = b0 + b1X + e1
- We test if SES (X) significantly predicts health outcomes (Y).
Hypothetical Scenario:
We’ll examine the relationship between:
- Causal Variable (X): Socioeconomic Status (SES)
- Mediating Variable (M): Access to Healthcare
- Outcome Variable (Y): Overall Health Outcomes
We hypothesize that SES (X) influences access to healthcare (M), which in turn influences overall health outcomes (Y). We want to test if access to healthcare mediates the relationship between SES and health outcomes.
1. Assumptions of Multiple Regression:
Before fitting the model, we must consider the assumptions of multiple regression:
- Linearity: The relationships between variables are linear.
- Independence of Errors: The errors (residuals) are independent.
- Homoscedasticity: The variance of errors is constant across levels of the predictor variables.
- Normality of Errors: The errors are normally distributed.
- No Multicollinearity: Predictor variables are not highly correlated.
We would need to check these assumptions using diagnostic plots and statistical tests (e.g., scatterplots, residual plots, VIF) after fitting the model.
2. Fitting the Mediation Model:
We will use a series of regression models to test for mediation, typically following Baron and Kenny’s (1986) approach, or a more robust approach such as bootstrapping.
- Model 1: Total Effect (X on Y):
Y = b0 + b1X + e1
- We test if SES (X) significantly predicts health outcomes (Y).