The German Intelligibility in Context Scale (ICS-G): reliability and validity evidence

In 2012 the Intelligibility in Context Scale (ICS) was published as a parent-report screening assessment that considers parents' perceptions of their children's functional intelligibility with a range of communication partners that differ in levels of authority and familiarity in real-life situations. To date, the ICS has been translated into 60 languages (including German).

To evaluate the psychometric properties of the German translation of the ICS ( = ICS-G), especially its reliability and validity, using four objective measures of speech sound disorder (SSD) severity: percentage of consonants correct (PCC); percentage of initial consonants correct (PICC); percentage of vowels correct (PVC); and percentage of phonemes correct (PPC).

Children who were typically developing (TD) and children with SSD (n = 181; 90 males, 81 females; mean age = 4.18 years, SD = 0.79 years, range = 3;0-5;11 years) were recruited through 13 kindergartens and 15 speech-language pathologists (SLPs) in Germany. All children's parents completed the ICS-G. To obtain an insight into the severity of SSD (n = 30), children's speech skills were assessed with PLAKSS-II. For the analysis of test-retest reliability the ICS-G was re-administered with a subsample of parents (n = 36) after 1 week.

The ICS-G had high internal consistency (α = .95, p < .001) and high test-retest reliability (r = .998, p < .001). The ICS-G total scores and item scores for both samples showed significant correlations, indicating good construct validity. Analyses revealed low but significant correlations with external factors (e.g., age, social class). Criterion validity was established through significant correlations between the ICS-G and scores for PCC (r = .43), PICC (r = .43), PVC (r = .62) and PPC (r = .47). The discriminatory ability of the ICS-G was indicated by significantly higher mean scores for the TD group (mean = 4.49, SD = 0.47) than the SSD group (mean = 3.97, SD = 0.63).

The overall good psychometric properties of the ICS-G support its use by SLPs for clinical and research purposes with German-speaking children.