Table 1.
Summary of issues before, during, and after mediation analysis
| Decisions made prior to mediation analysis |
| What is the best way to randomize participants? |
| Determine realistic randomization schema—realistically this often means only randomizing X |
| Ideally use “double randomization” and randomize participants to levels of both X and M |
| Determine if the use of blockage or enhancement designs is appropriate |
| When double randomization is not possible, use theory and prior research to address that Ignorability Assumptions regarding omitted variables are not violated |
| Which mediators should be included in the study? |
| Rely on action and conceptual theory to choose mediators |
| Are the measures reliable and valid? |
| Choose measures that have high levels of reliability if a mediated effect is hypothesized since unreliability can considerably reduce the power to detect the mediated effect |
| Ideally, minimize unreliability by using multiple indicators of the latent variable of interest (assuming the researcher has access to an adequately sized sample for such a model) |
| Insure that the measures reflect the hypothesized construct |
| What should our sample size be? |
| Mediation studies are often underpowered so conduct appropriate power analyses to determine that you will have enough power to detect a mediated effect |
| Consider timing or longitudinal effects for X to M and M to Y and other variables |
| Specify when X will affect M and when M will affect Y. Based on these ideas select times to measure these variables in a longitudinal study |
| Decisions made during mediation analysis |
| What statistical test should we conduct? |
| Determine the mediation model based on the research question of interest |
| Test mediators individually and all together. Include relevant moderators |
| Identify covariates to include in the models |
| Use the distribution of the product (PRODCLIN) or Bootstrapping methods to estimate the 95% confidence interval |
| Correct for measurement error if necessary |
| Decisions made following mediation analysis |
| What steps can we take in the next study to further understand the causal process by which our mediators cause change? |
| What are the limitations of the mediation study and what information would improve identification of a mediation process? |
| Discuss the veracity of the action theory and conceptual theory of the study |