Reliability and construct validity of the modified Finnish version of the 9-item Patient Health Questionnaire, and its’ content validity within biopsychosocial frame among female healthcare workers with sub-acute or recurrent LBP
Abstract Background: Healthcare workers have increased risk for chronic low back pain (LBP) leading to reduced workability. Depression, a highly prevalent, costly and disabling condition, is commonly seen in patients with sub-acute LBP. This study investigated the psychometric properties and content-validity of a modified 9-item Patient Health Questionnaire (PHQ-9-mFIN) in female healthcare workers with sub-acute LBP. Methods: Reliability (internal consistency, test-retest repeatability) was assessed with standard methods. Construct validity of the PHQ-9-mFIN was assessed as level of depression (PHQ-9-mFIN: 0-4 none, 5-9 mild, ≥10 at least moderate) against RAND-36 Health Survey, a valid measure of health-related quality of life (HRQoL). Content validity was determined as the strength of the association between the levels of PHQ-9-mFIN and the selected biopsychosocial factors. Results: The internal consistency of the PHQ-9-mFIN was high (Cronbach’s α=0.82) and the test-retest repeatability scores (n=65) fair: Pearson’s correlation 0.76, Kappa-value 0.42 for the diagnostic criterion (i.e. scores 0-9 vs. 10-27). Construct validity (Spearman correlation) against the Physical and Mental component items and their summary scales of the RAND 36 were much higher for the Mental (range -0.43 to -0.70 and -0.68) than for the Physical (range -0.06 to -0.41 and -0.24), respectively. There was a clear stepwise association (p<0.001) between the levels of depressive symptoms and General health (physical component, range 59.1 to 78.8). The associations with all items of the Mental components were strong and graded (p<0.001). All participants had low scores for Bodily pain regardless of the level of depressive symptoms. There was a strong association (p≤0.003) between levels of PHQ-9-mFIN and multisite pain, lumbar exertion and recovery after work days, neuromuscular fitness in Modified push-ups, workability, and fear of pain related to work. Conclusions: The PHQ-9-mFIN showed adequate reliability, and excellent construct and content validity among female healthcare workers with recurrent LBP and physically strenuous work. Trial registration: NCT01465698