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 (a) 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), (b) assess the reliability of the IES-IDs, and (c) compare it to an existing measure post-traumatic stress disorder 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 two 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 percent 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, but not the LANTs

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