Background and aims Low back pain (LBP) is common, and is a major health concern. Psychological consequences of LBP, such as depression, are significant barriers to recovery, but mechanisms for the development of depression are less well understood. One potential mechanism is the individuals’ Health Locus of Control (HLOC), i.e. perception of the level of control an individual has over their health. The aim of this study is to investigate the moderation effect of HLOC on the pain-depression pathway. Methods Cross sectional study of participants (n = 637) from two cohorts of primary care LBP patients. Two Structural Equation Model analysis groups were created (low perceived control, and high perceived control), based on the HLOC Internality Scale. The path model consisted of pain intensity and disability as exogenous predictors, pain interference (endogenous mediator), bothersomeness (endogenous predictor) and depression (outcome). Critical ratio difference tests were applied to the coefficients using pairwise comparisons. Results Both models had an acceptable model fit. Critical ratio tests indicated a significant (p < 0.05) moderation effect, with stronger pathway coefficients for depression for those who report low Internality (β 0.48), compared to those with high Internality (β 0.26). Conclusions HLOC Internality significantly moderates the pain-depression pathway in those with back pain, meaning that those who have a low perception of control report greater levels of depression. This may signify a potential factor that may predict depression among people with pain, and could potentially be a target for intervention
