Page 68 - Post-traumatic stress disorder in adults with mild intellectual disability: Screening, assessment, and brief intensive EMDR therapy

Chapter 3
Validity and reliability of the Trauma Screener-Intellectual Disability
proxy version
The validity of the TS-ID proxy version was examined by calculating the AUC
using ROC analysis. AUC was assessed by comparing the total symptom
frequency score of the TS-ID proxy with the final outcome of the DITS-ID
(i.e. yes or no PTSD). The AUC value was .60 (N = 91, SD = .06, p = .10),
indicating low validity of the TS-ID proxy version for distinguishing between
individuals with and without a PTSD diagnosis. Cronbach›s alpha for the
total symptom frequency score of the TS-ID proxy version (section two)
was .93, indicating high internal consistency.
Because the ROC analyses indicated that the TS-ID proxy version is not a
valid instrument for detecting PTSD in people with MID-BIF, a cut-off value
was not determined for the TS-ID proxy version.
Discussion
The TS-ID adult version demonstrated high internal consistency and
excellent validity in distinguishing PTSD in adults with MID-BIF. A cut-off
value of 18 is recommended for the adult version of the TS-ID, with which
an optimal balance between sensitivity and specificity was achieved. While
demonstrating high internal consistency, the TS-ID proxy version did not
have significant validity in distinguishing individuals with and without a
PTSD diagnosis.
The effectiveness of the TS-ID proxy version in assessing adults with MID-
BIF may be limited by the lack of knowledge of parents (Kooij et al., 2025)
and professional caregivers regarding their trauma history (Hoogstad et
al., 2023). Furthermore, three of the four PTSD symptom clusters consist
of symptoms about thoughts and feelings as a result of experiencing a
traumatic event, that is, Intrusions (cluster B), Avoidance (cluster C) and
Negative alterations in cognitions and mood (cluster D). Adults with MID-
BIF communicate less clearly about their thoughts and feelings with their
caregivers (Hassiotis & Turk, 2012; Summers et al., 2017). Therefore, it
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