Measuring symptoms of post-traumatic stress disorder in people with intellectual disabilities: the development and psychometric properties of the Impact of Event Scale-Intellectual Disabilities (IES-IDs)

Background: The aims of the study were to (1) revise the Impact of Event Scale–Revised for use with people with intellectual disabilities (IDs), creating the Impact of Event Scale–Intellectual Disabilities (IES-IDs), (2) assess the reliability of the IES-IDs, and (3) compare the IES-IDs to an existing measure trauma-related symptomatology, namely the Lancaster and Northgate Trauma Scale (LANTS), along with measures of anxiety and depression.

Methods: Forty adults with IDs who had experienced at least one traumatic event were recruited and completed the IES-IDs and the LANTS on two occasions, separated by 2 weeks. Participants also completed the Glasgow Depression Scale and the Glasgow Anxiety Scale, along with the Trauma Information Form which was used to collect information about trauma history.

Results: Fifteen per cent of the sample had encountered five or more traumatic events. The IES-IDs and the LANTS had good to excellent internal consistency and test–retest reliability. Both measures correlated with self-report measures of depression and anxiety, although the strength of this correlation was greater with the LANTS. There was a significant positive correlation between trauma frequency and the IES-IDs, while trauma frequency did not correlate with the LANTS.

Conclusions: Both the IES-IDs and the LANTS appear to have good reliability.