Examining item bias in the anxiety subscale of the Hospital Anxiety and Depression Scale in patients with chronic obstructive pulmonary disease.

The Hospital Anxiety and Depression Scale (HADS) is a widely used screening instrument for depression and anxiety in medically compromised patients. The purpose of this study was to examine the differential item functioning (DIF) of the anxiety subscale of the HADA (HADS-A). A research assistant administered the HADS-A to 166 Chinese patients with chronic obstructive pulmonary disease (COPD) who were consecutively admitted to a rehabilitation hospital. Although the HADS-A was overall uni-dimensional, there were one mute item and two items with borderline misfit. Only one item had a DIF for arterial oxygen saturation. No item had DIF for other indicators of the severity of COPD. In conclusion, this study found that for one item the HADS-A has significant item bias for the severity of disease in patients with COPD.