RQ1: Long-Term Effectiveness of Online Self-Help Training in Reducing FCR and PD
PD
To answer the first research question (i.e., do the intervention and CAU group differ in the change in FCR/PD over time), a multi-group second-order latent growth model was estimated. A second-order growth model estimates individual growth curves for each participant based on the individual FCR or PD item scores. A multi-group extension allows testing differences between interventions in the growth model parameters. The parameter of main interest was the average latent slope estimate in both the intervention and CAU groups and whether these differed between the groups. We estimated the model separately for FCR and PD, because the multivariate model for both FCR and PD did not converge (most likely, the model was too large for the data). Each of the FCR/PD models was built in five steps, first testing the assumption of longitudinal measurement invariance, followed by two models to test the null hypothesis that the difference between the groups in the latent slope is equal to zero. Growth model analyses were estimated with maximum likelihood estimation, using R statistical software (version 3.5.3), with software packages Lavaan (R package for Structural Equation Modeling, version 0.6-9) and BaylorEdPsych (R-package used for checking missing data for random occurrences, version 0.5) [