Changes to statistical methods because of baseline analyses
REGRESSION
Baseline comparisons showed main effects of country (see Results of Baseline data below), whereby the children in the Dutch sample consistently outperformed the Belgian children in timed letter-sound knowledge, phonological awareness, and rapid automatised naming at T1. Therefore, contrary to the initial analysis plan, the Belgian and the Dutch samples were used independently to evaluate all research questions. This doubled the number of planned analyses from 7 to 14 models and reduced statistical power due to smaller group sizes.In addition, the described approach did not yield answers for research question three in that none of the game exposure measures ended up as relevant predictors (see Results of Question 3: Intervention properties below). In an explorative approach, we therefore re-combined children from both countries to increase statistical power, merged all exposure measures by means of a principal component analysis and fitted two additional models for the outcome of reading fluency using non-linear mixed effects regression (Generalized Additive Model; 