Monitoring somatic symptoms in patients with mental disorders: Sensitivity to change and minimal clinically important difference of the Somatic Symptom Scale - 8 (SSS-8)

Abstract

Objective: The SSS-8 is a brief questionnaire for the assessment of somatic symptom burden. This study examines its sensitivity to change and the minimal clinically important difference (MCID) in patients with mental disorders.

Method: 55 outpatients with mental disorders completed the SSS-8 and measures of anxiety, depression, and disability before and after receiving treatment. Effect sizes and correlations between the change scores were calculated. The MCID was estimated using a one standard error of measurement threshold and the change in disability as an external criterion.

Results: There was a medium decline in somatic symptom burden for the complete sample (n=55, d_z=0.53) and a large decline in a subgroup with very high somatic symptom burden at baseline (n=11, d_z=0.94). Decreases in somatic symptom burden were associated with decreases in anxiety (r=0.68, p<0.001), depression (r=0.62, p<0.001) and disability (r=0.51, p<0.001). The MCID was estimated as a 3-point decrease.

Conclusion: The SSS-8 is sensitive to change. A 3-point decrease reflects a clinically important improvement. Due to its brevity and sound psychometric properties, the SSS-8 is useful for monitoring somatic symptom burden.

Keywords: Minimal clinically important difference; SSS-8; Sensitivity to change; Somatic symptom burden.