Cross-sectional validation of the Rasch-based Depression Screening (DESC) in a mixed sample of patients with mental and somatic diseases.

BACKGROUND: The study aimed to cross-validate the psychometric properties of the two parallel versions of the "Rasch-based Depression Screening (DESC)" in a mixed clinical sample of patients with mental disorders and somatic diseases. Additionally, it was intended to confirm the initially proposed cut-off scores.

METHODS: One hundred eleven inpatients from the Departments of Psychiatry (n=50), Cardiology (n=39) and Otorhinolaryngology (n=22) were examined. Accordance to Rasch model assumptions was determined by analyzing item infit and outfit as well as unidimensionality and local independence via residual principal components factor analysis (PCFA). Furthermore, separation, reliability and the targeting were considered. Differential item functioning (DIF) was investigated with regard to gender, age and clinical group. Finally, receiver operating characteristics (ROC) curves analyses were conducted and parallel test reliability was calculated.

RESULTS: Item and person separation and reliability were good with separation values being above 2.90 and reliability exceeding being .90. Rasch model fit was good for all items except for the two items "sad" and "hopeless" displaying slight misfit. Targeting was appropriate with a person mean of -1.6 (DESC-I) and -1.5 (DESC-II) reflecting as expected that the two DESC versions were in average to easy for a mixed sample of patients with mental disorders and somatic. PCFA showed unidimensionality and local independence: The Rasch dimension "depression" explained 84.8% (DESC-I) and 82.2% (DESC-II) of the observed variance. No DIF was found. ROC curves confirmed the proposed cut-off score of 12 points. The area under the curve amounted to .91 for both DESC forms. The Youden index was 75.5 for DESC-I and 75.7 for DESC-II. A high parallel test reliability of .94 showed virtual equivalence of both DESC forms.

CONCLUSIONS: Results of the present study support the good psychometric properties of both DESC forms in patients with mental disorders and somatic diseases. This study confirmed the cut-off scores that had already been determined in former patient samples. Thus, both DESC forms can be used validly as screening instruments for depression in clinical practice.