Table 1. Simulation Scenario 1 — The simulation model is the standard unidirectional mediation model.
The parameter estimates and the coverage percentages are based on 1000 replicates using the bidirectional and unidirectional mediation models.
| Parameter | True Value | Bidirectional Mediation Model | Uni-M-Y1 |
|---|---|---|---|
| β12 | 0.75 | 0.76 (94.30%) | 0.75 (94.20%) |
| β21 | 0.00 | −0.01 (95.40%) | 0.00 (100%)a |
| γ21 | −0.25 | −0.25 (95.90%) | −0.25 (94.90%) |
| γ32 | −0.25 | −0.25 (95.80%) | −0.25 (95.50%) |
| Direct Effect of X1 on Y2 | 0.75 | 0.75 (94.40%) | 0.75 (92.60%) |
| Direct Effect of X1 on Y1 | 0.50 | 0.51 (96.10%) | 0.50 (95.60%) |
| Indirect Effect of X1 on Y2 through Y1 | 0.38 | 0.38 (95.10%) | 0.38 (93.80%) |
| Indirect Effect of X1 on Y1 through Y2 | 0.00 | −0.03 (96.70%) | 0.00 (100%)a |
Uni-M-Y1 is the univariate mediation model: X1 is the initial variable, Y1 is the mediator, and Y2 is the outcome.
a
The parameters β21 and indirect effect of X1 on Y1 through Y2 are not modeled in the standard unidirectional model, Uni-M-Y1; therefore, these parameters are assumed to be zero.