['The recovery of patients with chronic low back pain (LBP) is slow. Furthermore, it is recently proposed that chronic LBP needs a prognostic approach to determine who will develop clinically significant back pain. Therefore, it is imperative to identify prognostic factors that are mostly seen in chronic LBP patients at an early stage. This may give clinicians tailored advice to prevent chronicity or may refer to a specific intervention.', 'To investigate the contribution of demographic, work, clinical, and psychosocial variables, including new prognostic variables as changes in pain intensity and disability status, on the development of chronic LBP.', 'Prospective cohort data by merging data from three randomized trials (secondary analyses).', 'Workers (n=628) on sick leave because of subacute nonspecific LBP.', 'Chronic LBP for longer than 6 months (functional measure).', 'Potential prognostic variables were demographic, work, clinical, and psychosocial characteristics (self-report measures). We also included as prognostic variables a clinically relevant change in pain intensity and disability status. For the selection of variables and prognostic models, bootstrapping techniques were used in combination with multivariable logistic regression. The explained variance and discrimination were used to evaluate the clinical performance of the models.', 'The variables most strongly related to chronic LBP were as follows: no clinically relevant change in pain intensity and in disability status in the first 3 months, a higher pain intensity score at baseline, and a higher score for kinesiophobia. This prognostic model had a bootstrap-corrected explained variance of 37% and a discriminative ability (c index) of\xa00.80.'] Is the prognosis of chronic low back pain determined by changes in pain and disability in the initial period?