Comparison of percentage of syllables stuttered with parent-reported severity ratings as a primary outcome measure in clinical trials of early stuttering treatment

Purpose: This report investigates whether parent-reported stuttering severity ratings (SRs) provide similar estimates of effect size as percentage of syllables stuttered (%SS) for randomized trials of early stuttering treatment with preschool children.
Method: Data sets from 3 randomized controlled trials of an early stuttering intervention were selected for analyses. Analyses included median changes and 95% confidence intervals per treatment group, Bland–Altman plots, analysis of covariance, and Spearman rho correlations.
Results: Both SRs and %SS showed large effect sizes from pretreatment to follow-up, although correlations between the 2 measures were moderate at best. Absolute agreement between the 2 measures improved as percentage reduction of stuttering frequency and severity increased, probably due to innate measurement limitations for participants with low baseline severity. Analysis of covariance for the 3 trials showed consistent results.
Conclusion: There is no statistical reason to favor %SS over parent-reported stuttering SRs as primary outcomes for clinical trials of early stuttering treatment. However, there are logistical reasons to favor parent-reported stuttering SRs. We conclude that parent-reported rating of the child’s typical stuttering severity for the week or month prior to each assessment is a justifiable alternative to %SS as a primary outcome measure in clinical trials of early stuttering treatment.