Data Analysis Plan
Linear mixed models were used to evaluate whether (a) BT would have
worse SIP and social skills over time compared to ST and (b) whether
social skills and accuracy in recognizing facial expressions and others’
social intentions were positively associated with peer relationship
quality. For longitudinal designs with two time points and data missing
at random, maximum likelihood estimation used in mixed models produces
less biased estimates than least squares approaches [19]. Thus, we
used a random intercept model with restricted maximum likelihood
estimation to test our hypotheses. All continuous predictors were
grand-mean centered to aid the interpretation of coefficients.
In the model for hypothesis (a), DANVA-2, Irony & Empathy, and SSiS
were entered as outcome variables in three separate models, while time,
group and their interaction were entered as predictors. Three models
were run for hypothesis (b) that differed only in terms of the specific
predictor variable tested. The three predictors included baseline values
of SSiS, DANVA-2, and Irony & Empathy. For example, for the model
evaluating the influence of baseline social skills, PROMIS Pediatric
Peer Relationships was the outcome variable, while time, baseline SSiS,
group and a 3-way interaction between them were entered as predictors.
We also conducted two post hoc analyses in the BT group, where we
evaluated the moderating effect of baseline time-since-diagnosis on
Irony & Empathy and social skills. Examination of diagnostic plots at
levels 1 and 2 showed that models met assumptions of normality,
linearity, independence and constant variance. The nlme package from the
R Statistical Computing Language was used to run the linear mixed models
and the sjPlot R package was used to produce tables and graphs of simple
slopes.
RESULTS