Validation of an item bank for detecting and assessing psychological distress in cancer patients.

OBJECTIVE: To validate an item bank for assessing and detecting psychological distress in cancer patients by (1) identifying whether additional items are required in the full item bank; (2) identifying any item bias in the existing item bank; (3) linking levels of distress against thresholds derived from gold-standard psychiatric interviews (PSE/SCAN/SCID).
METHOD: A Rasch analysis was conducted on a heterogeneous sample of cancer patients (n=4919) who had completed a combination of eight psychological distress screening instruments. A subset of patients had completed a psychiatric interview along with the HADS (n=381) or PHQ-9 (n=440). Item thresholds were plotted along the latent trait. Furthermore, items were assessed for differential item functioning (DIF) by age and gender. Finally, optimum thresholds were derived for the HADS and PHQ-9 and plotted along the latent trait distribution for the entire item bank. RESULT: Item thresholds exceeded the range of person measures, although a gap was still present along the latent trait. No DIF was observed for either age or gender. Putative cut-offs were derived for the item bank detecting moderate to severe levels of psychological distress.
CONCLUSION: The item bank covers the majority of levels of emotional distress reported by cancer patients. Additionally, initial thresholds have been derived on the item bank, which correspond to a formal psychiatric assessment. Further work is required to ascertain the stability of the item bank over time and by diagnosis and stage of disease, as well as to determine additional thresholds for levels of distress. (c) 2008 John Wiley & Sons, Ltd.