Robin van Rijthoven

66 Chapter 3 Correlations among all study variables are presented in Table 3.2. As can be seen, phonological awareness was significantly correlated with word decoding posttest percentile scores, and word spelling posttest percentile scores. Rapid automatized naming correlated significantly with word decoding pretest and posttest percentile scores, whereas verbal workingmemory did not correlate significantly with any criterion measure. With respect to the covariates, both perceptual cognitive skills and spelling pretest scores were significantly related to spelling posttest percentile scores. Figure 3.1. Boxplots of Pretest and Posttest Scores of Word Decoding, Pseudoword Decoding, and Word Spelling. Phonics through spelling intervention effects First, the effect of the intervention was established by determining response to intervention for each child. Based on the normal distribution and the correction for time, typically developing children would have the same percentile score at pre- and posttest. Positive mean change scores per session among the children with dyslexia therefore would indicate a response to intervention. Table 3.1 presents the descriptive statistics for the percentile scores and the change scores for all dependent variables. The mean change scores are positive for all dependent measures. Paired-sample t-tests, using Holm–Bonferroni correction (Holm, 1979), were used to test whether a change was significant. Holm–Bonferroni procedure was used to adjust the critical p-value to control for the Type 1 error (see Abdi, 2010). Pseudoword posttest percentile scores were significantly higher than pretest percentile scores (t (43) = -3.927, adjusted p = .017, d = 0.51). Similar positive effects were found for posttest versus pretest percentile scores of word reading (t (52) = -3.453, adjusted p = .025, d = 0.47) and word spelling (t (52) = -3.137, adjusted p = .050, d = 0.59). Pretest and posttest differences are depicted in boxplots in Figure 3.1. Out of all children, 49.1% were no longer among the lowest 10% for spelling. For pseudoword reading this was 26.1% and for word reading 29.6%.