Pain intensity was measured using the mean of three 0–10 numerica

Pain intensity was measured using the mean of three 0–10 numerical rating scales for least and usual LBP over the previous 2 weeks, and current LBP intensity; scores of five or more were defined as high pain intensity (Dunn et al., 2010). Functional disability was measured using the modified 23-item RMDQ (Patrick et al., 1995) with high functional disability defined as a score CX-5461 nmr greater than 14 (Cherkin et al., 1998). Bothersome LBP was defined if people rated their pain during the previous 2 weeks as very much or extremely bothersome

(Dunn and Croft, 2005). Information on previous LBP, and presence or absence of leg pain, distal leg pain and upper body pain (shoulder, arm, neck or head) over the previous 2 weeks was also collected. Probable cases of clinical anxiety or depression were defined as scores of eleven or more on the HADS (Zigmond and

Snaith, 1983). People were classified as catastrophisers if they felt that the pain was terrible and was never going to get any better based on a modified item from the Coping Strategies Questionnaire (Rosenstiel and Keefe, 1983). The use of single items to measure this construct has since been validated (Jensen et al., 2003), and the construct validity of this particular question has been established (Hill et al., 2008). Fear-avoidance beliefs were recorded if people stated that they could not do all the things normal people do because it is too easy for them to get injured, an item modified from the Tampa Scale for Kinesiophobia (Kori et al., 1990) and recommended for use as a single item (Vlaeyen et al., 2001). Self-reported health status was measured as reporting fair or poor on the general health perceptions question, and vitality was measured using with the vitality

sub-scale, from the Short Form-36 questionnaire (Ware, 2000). For vitality, people below the bottom tertile (with scores less than 25) were defined as having low vitality. Outcome 12-months after baseline was measured using the Chronic Pain Grade (CPG; Von Korff et al., 1992). This classifies individuals into grades of chronic LBP: 0 (pain free), I (low disability, low intensity), II (low disability, high intensity), III (high disability, moderately limiting) and IV (high disability, Cell press severely limiting). A poor outcome is defined here as CPG IV (highly disabling and severely limiting LBP). This measure was chosen as the outcome as it was not included as a prognostic indicator in the current analysis. Participants who returned the complete baseline and 12-month questionnaires were included in this analysis. Crude RRs with 95% confidence intervals (CI) were calculated for the associations between all potential prognostic indicators at baseline and 12-month outcome. Indicators that had a statistically significant association with outcome were then adjusted for potential confounders using Cox regression models with a constant time variable (Thompson et al., 1998).

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