| No-history (N) | No episode of back pain sufficient to cause time off work or to prevent activities of daily living in past 5 years |
| Chronic (CH) | Continuous or intermittent pain sufficient to cause time off work or to prevent activities of daily living over last 12 months. At least one episode in the last 3 months |
| Past history (PH) | At least one episode in the last 5 years severe enough to cause time off work or to prevent activities of daily living, but no such attack in the last 2 years |
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