Psychometric Evaluation of the Rasch-Based Depression Screening in Patients With Neurologic Disorders

Forkmann T, Norra C, Wirtz M, Gauggel S, Boecker M. Psychometric evaluation of the Rasch-based depression screening in patients with neurologic disorders.

Objectives

To provide a first evaluation of the Rasch-Based Depression Screening (DESC) in consecutive patients with neurologic disorders.

Design

Cross-sectional study.

Setting

Hospital specializing in neurologic disorders.

Participants

Eligible patients (N=323; mean age ± SD, 53.4±17.2y; 49.3% women) age 18 years and older.

Interventions

Not applicable.

Main outcome Measures

DESC with 2 parallel versions.

Results

Both versions of the DESC showed good item separation (DESC-I=4.96; DESC-II=4.94) and person separation (DESC-I=2.01; DESC-II=2.14) as well as item separation reliability (DESC-I=.96; DESC-II=.96) and person separation reliability (DESC-I=.80; DESC-II=.82). All items fit the Rasch model (infit and outfit mean squares ≤1.3). There were no signs of violation of unidimensionality. One item of DESC-I showed differential item functioning because of age and 1 item because of sex. Parallel test reliability of the 2 DESC forms was r equal to .92.

Conclusions

The DESC shows good psychometric characteristics that suggest high psychometric quality of the instrument in patients with neurologic disorders. Differential item functioning on single items needs further examination but should not substantially interfere with the valid interpretation of DESC sum scores.