An evaluation of the psychometric properties of the adapted PHQ-9 and GAD-7 outcome measures for use with adults with intellectual disability

Background: People with intellectual disability often face barriers accessing mainstream psychological services due to a lack of reasonable adjustments, including the absence of adapted versions of routine outcome measures. Adapted versions of the Patient Health Questionnaire-9 (PHQ-9) and the Generalised Anxiety Disorder-7 (GAD-7) have been created for adults with ID.

Aims: This study aims to evaluate the psychometric properties of the adapted PHQ-9 and GAD-7.

Method: The adapted PHQ-9 and GAD-7 and the Glasgow Depression and Anxiety Scales (GDS-ID, GAS-ID) were administered to 47 adults (n=21 clinical group; n=26 community group) with ID. Cross-sectional design and between-group analyses tested for discriminant validity. Concurrent and divergent validity was tested using correlational designs. Reliability was investigated by internal consistency and test–retest analysis.

Results: The clinical group scored significantly higher on the adapted PHQ-9 (t₄₅=–2.28, p=.03, 95% CI [–7.09, –.45]) and GAD-7 (t₄₅=–3.52, p=.001, 95% CI [–7.44, –2.02]) than the community group, evidencing discriminant validity. The adapted PHQ-9 correlated with the GDS-ID (r₄₇=.86, p<.001) and the adapted GAD-7 correlated with the GAS-ID (r₄₆=.77, p<.001). The adapted PHQ-9 (Cronbach’s α=.84, ICC=.91) and GAD-7 (Cronbach’s α=.86, ICC=.77) had good internal consistency and test–retest reliability.

Conclusions: Preliminary research suggests the adapted PHQ-9 and GAD-7 are valid and reliable measures. They could provide a reasonable adjustment for the minimum dataset used in NHS Talking Therapies and can be easily administered in routine clinical practice. Further work to establish additional psychometric properties is now required.