Construct validity of the Depression and Somatic Symptoms Scale: evaluation by Mokken scale analysis

Area of Science:

• Psychiatry
• Psychometrics
• Mental Health Assessment

Background:

• Previous studies on the Depression and Somatic Symptoms Scale (DSSS) used classical test theory, leaving its construct validity and dimensionality uncertain.
• The DSSS is a freely available scale for assessing depression and somatic symptoms.

Purpose of the Study:

• To evaluate the dimensionality and construct validity of the DSSS using Mokken scale analysis (MSA).

Main Methods:

• A sample of 214 psychiatric outpatients with mood and anxiety disorders completed the DSSS.
• Mokken scale analysis (MSA) was employed to assess the scale's dimensionality.

Main Results:

• All 22 items of the DSSS demonstrated moderate unidimensionality (H=0.403), supporting its construct validity.
• The DSSS was divided into four subscales: General Somatic Scale (GSS), Melancholic Scale (MS), Muscular Pain Scale (MPS), and Chest Symptom Scale (CSS).
• The MS, MPS, and CSS were identified as strong reliable Mokken scales, while the GSS was a weak reliable Mokken scale.

Conclusions:

• The DSSS is a psychometrically sound instrument for measuring depression and somatic symptoms in adult psychiatric outpatients.
• The summed score of the DSSS and its four subscales are valid statistical measures.
• Further research is recommended to replicate the identified four subscales of the DSSS.