Index to Chiropractic Literature
Index to Chiropractic Literature
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ID 21231
  Title Illustrating risk difference and number needed to treat from a randomized controlled trial of spinal manipulation for cervicogenic headache
Journal Chiropr & Osteopat. 2010 ;18(9):Online access only 8 p
Peer Review Yes
Publication Type Randomized Controlled Trial
Abstract/Notes BACKGROUND: The number needed to treat (NNT) for one participant to benefit is considered a useful, clinically meaningful way of reporting binary outcomes from randomized trials. Analysis of continuous data from our randomized controlled trial has previously demonstrated a significant and clinically important difference favoring spinal manipulation over a light massage control.

METHODS: Eighty participants were randomized to receive spinal manipulation or a light massage control (n = 40/group). Improvements in cervicogenic headache pain (primary outcome), disability, and number in prior four weeks were dichotomized into binary outcomes at two thresholds: 30% representing minimal clinically important change and 50% representing clinical success. Groups were compared at 12 and 24-week follow-up using binomial regression (generalized linear models) to compute the adjusted risk difference (RD) between groups and number needed to treat (NNT) after adjusting for baseline differences between groups. Results were compared to logistic regression results.

RESULTS: For headache pain, clinically important improvement (30% or 50%) was more likely for spinal manipulation: adjusted RD = 17% to 27% and NNT = 3.8 to 5.8 (p = .005 to .028). Some statistically significant results favoring manipulation were found for headache disability and number.

CONCLUSION: Spinal manipulation demonstrated a benefit in terms of a clinically important improvement of cervicogenic headache pain. The use of adjusted NNT is recommended; however, adjusted RD may be easier to interpret than NNT. The study demonstrated how results may depend on the threshold for dichotomizing variables into binary outcomes. TRIAL REGISTRATION: NLM identifier NCT00246350.

This abstract is reproduced with the permission of the publisher. Click on the above link for free full text.

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