ILS Properties

Reliability and Validity
Inter-rater reliability scores were assessed across 11 clients on seven consecutive days (n = 77). Convergent validity as demonstrated with the Vineland Adaptive Behavior Scale and the AAMD – Adaptive Behavior Scale. Test-retest stability was demonstrated by correlational analysis of admission to discharge ILS scores (n = 344). Total ILS score reliability was R² = 0.85, behavior sub-scale, R² = 0.77, and ADL scale, R² = 0.93. Inter-observer reliability was not determined for the initiation sub-scale. The ILS total score correlation with the Vineland was R² = 0.82 and AAMD scale, R² = 0.87. Test-retest stability was determined to be R² = 0.72.

Psychometric Properties
Factor analysis (with Varimex rotation) generated a four factored model matrix (n = 5250). The Kaiser-Meyer-Olkin Measure of Sampling Adequacy was 0.94 (marvelous) and the Bartlett Test of Sphericity was 107628.38, Sig = 0.00 (scale items, independent). Factor 1 (Self-Care) consisted of items related to performance of ADL's. The top three Self-Care items were hygiene/grooming, dressing and toileting (R² > 0.85). Factor 2 (Directed Aggression) consisted of behaviors related to directed aggression. The top two items were property abuse and sexually aberrant behavior (R² > 0.76). Factor 3 (Environmental Care) consisted of items related to care of the living environment. The top item was shopping (R² > 0.76). Factor 4 (Protective Task Avoidance) consisted of behaviors related to task avoidance, which were deemed to be primarily self-protective. The top three items were self-abuse, perseverative speech and exiting (R² > 0.77).

Statistical fit was examined using step-wise regression analysis of the four factor model. Factor 1 (Self-Care) loaded at an adjusted R² of 0.50, factor 4 (Protective Task Avoidance) increased the adjusted R² by 0.15, factor 2 (Directed Aggression) increased the adjusted R² by 0.14 and factor 3 (Environmental Care) increased the adjusted R² by 0.01. Total adjusted R² was 0.80, with a standard error of 10.3 (n = 5250).