Illustrating risk difference and number needed to treat from a randomized controlled trial of spinal manipulation for cervicogenic headache

Table 3 Participants obtaining 30% and 50% improvement in outcomes: odds ratio*

Improvement criterion		SMT (n = 36)	LM (n = 39)	adjusted odds ratio (95% CI)	P
Cervicogenic headache pain scale †
30%	12 wk	47%	38%	2.2 (0.8, 6.0)	.142
	24 wk	58%	49%	2.3 (0.8, 6.5)	.122
50%	12 wk	42%	23%	3.0 (1.1, 8.3)	.033
	24 wk	42%	23%	3.6 (1.3, 9.7)	.011
Cervicogenic headache number (in last 4 wk)
30%	12 wk	72%	51%	4.4 (1.3, 14.3)	.015
	24 wk	78%	62%	3.1 (0.9, 11.2)	.082
50%	12 wk	64%	46%	2.6 (0.9, 7.5)	.067
	24 wk	61%	51%	1.9 (0.7, 5.2)	.225
Cervicogenic headache disability scale †
30%	12 wk	64%	51%	2.0 (0.7, 5.7)	.193
	24 wk	61%	64%	0.9 (0.3, 2.4)	.803
50%	12 wk	64%	36%	3.8 (1.3, 11.0)	.014
	24 wk	56%	38%	2.2 (0.9, 5.9)	.102

SMT - spinal manipulative therapy; LM - light massage; NNT - number needed to treat
* Outcomes are presented for the 12-week (short-term) and 24-week (intermediate-term) follow-ups. The SMT and LM group percentages are unadjusted. Missing data were imputed except for five participants with no follow-up data. Odds ratios were adjusted for differences between groups in the baseline value of the outcome and all randomization variables. Ratios greater than 1.0 favor spinal manipulation.
† Modified Von Korff scale (scored from 0 to 100 points before dichotomization).

ISSN: 2045-709X