Brief screening questions for depression in chiropractic patients with low back pain: identification of potentially useful questions and test of their predictive capacity

BACKGROUND: Depression is an important prognostic factor in low back pain (LBP) that appears to be infrequent in chiropractic populations. Identification of depression in few patients would consequently implicate screening of many. It is therefore desirable to have brief screening tools for depression. The objective of this study was to investigate if one or two items from the Major Depression Inventory (MDI) could be a reasonable substitute for the complete scale. METHODS: The MDI was completed by 925 patients consulting a chiropractor due to a new episode of LBP. Outcome measures were LBP intensity and activity limitation at 3-months and 12-months follow-up. Single items on the MDI that correlated strongest and explained most variance in the total score were tested for associations with outcome. Finally, the predictive capacity was compared between the total scale and the items that showed the strongest associations with outcome measures. RESULTS: In this cohort 9% had signs of depression. The total MDI was significantly associated with outcome but explained very little of the variance in outcome. Four single items performed comparable to the total scale as prognostic factors. Items 1 and 3 explained the most variance in all outcome measures, and their predictive accuracies in terms of area under the curve were at least as high as for the categorised complete scale. CONCLUSIONS: Baseline depression measured by the MDI was associated with a worse outcome in chiropractic patients with LBP. A single item (no. 1 or 3) was a reasonable substitute for the entire scale when screening for depression as a prognostic factor.