Properties of the Sickness Questionnaire in an Australian sample with chronic medically unexplained symptoms

Evaluating the construct validity and internal consistency of the Sickness Questionnaire in a Swedish sample of adults with longstanding pain

OBJECTIVES

Low-grade inflammation is a possible contributing factor in the development and persistence of chronic primary pain syndromes. Related to inflammatory activity is sickness behavior, a set of behavioral responses including increased pain sensitivity, fatigue, malaise, fever, loss of appetite, as well as depressive behavior and anhedonia. To capture these behavioral responses and their relation to longstanding pain, psychometrically sound self-report questionnaires are needed. The Sickness Questionnaire (SicknessQ) was developed to assess self-reported sickness behavior based on studies on acute immune activation while maintaining relevance for persistent conditions. The aim of the current study was to evaluate aspects of the validity and reliability of the SicknessQ in a Swedish sample of persons with longstanding pain.

METHODS

Aspects of construct validity were evaluated by means of performing a confirmatory factor analysis (CFA) (testing structural validity) and by relevant hypothesis testing i.e., that ratings of sickness behavior in combination with other related factors (e.g., depression and anxiety) would be significantly related to ratings of avoidance. Reliability was evaluated by means of analyzing the internal consistency of items.

RESULTS

Following the CFA, a non-significant Chi-Square test (χ2 [32, N=190] = 42.95, p=0.094) indicated perfect model fit. Also, the relative fit indices supported adequate model fit (CFI = 0.978; TLI = 0.969; RMSEA = 0.0430). Sickness behavior (p<0.0001), depression (p<0.05) and pain duration (p<0.05) significantly contributed to the regression model, explaining 45% of the total variance in avoidance. Internal consistency was adequate, as indicated by a Cronbach's α value of 0.82 for the entire questionnaire.

CONCLUSIONS

Results indicate that the SicknessQ has adequate structural validity as well as adequate internal consistency, and is significantly associated with avoidance. The SicknessQ appears to have utility as a self-report questionnaire to assess symptoms of sickness behavior for adults with longstanding pain.

Sickness Questionnaire: A two-factor instrument reflecting physical and mental symptoms in the Chinese context

The Sickness Questionnaire (SicknessQ) is a 10-item inventory used to measure sickness-related symptoms. This study extended its psychometric properties in the Chinese context. A total of 992 clinical and non-clinical participants from three samples were included. Exploratory and confirmatory factor analyses indicated a 9-item two-factor structure (mental and physical symptoms) of the Chinese version of Sickness Questionnaire (SicknessQ-C). The internal consistency of the two subscales in this instrument ranged from .71 to .85. The incremental and predictive validities of SicknessQ-C demonstrated that this instrument contributed more to explaining the variance of flourishing than the measurement of negative emotion symptoms.