Caregiver's concerns-quality of life scale (CC-QoLS): development and evaluation of psychometric properties.

We have developed a Caregiver's Concerns-Quality of Life Scale (CC-QoLS) for adults with intellectual disabilities (ID) who exhibit aggressive behaviour. The CC-QoLS is a brief (8 items in each subscale, CC and QoL respectively) proxy measure completed by caregivers. This is a specific health related quality of life instrument (HRQoL) combined with measures of caregiver's concerns for use as an outcome measure to assess clinical and cost effectiveness of interventions for aggression in adults with ID. The CC-QoLS was found to have good face validity and very good test-retest reliability with an ICC of 0.81 for CC (range 0.46-0.83 across items) and 0.80 for QoL (range 0.65-0.81 across items). Similarly, the scale had good inter-rater reliability with an ICC of 0.67 for CC (range 0.31-0.63 across items) and 0.63 for QoL (range 0.31-0.65 across items). Internal consistency for each subscale was also good (Cronbach's alpha was 0.85 for CC and 0.80 for QoL; Split-half Spearman-Brown was 0.81 for CC and 0.70 for QoL). Furthermore, the scale showed good concurrent validity with measures of severity of aggressive behaviour, namely Modified Overt Aggression Scale (MOAS) (CC: r=0.4; p≤0.01 and QoL: r=-0.2; p≤0.05) and Aberrant Behavior Checklist-Irritability subscale (ABC-I) (CC: r=0.5; p≤0.01 and QoL: r=-0.02; p≤0.05) as well as Caregiver's Uplift and Burden Scale score (<0.05). We believe that the CC-QoLS is a user friendly, easy to complete, first-ever HRQoL measure for adults with ID and aggressive behaviour with very good psychometric properties.