Table 5

Analysis of effect size, heterogeneity, and ANOVA testing of difference by length of follow-up.

	Length of Follow-Up	Number of Studies Included in This Analysis	Effect Size	Lower Limit	Upper Limit	Higgins I ² Statistic of Heterogeneity	Variance	Standard Error	Number of Patients
Oswestry Disability Index	More than 2 y	45	0.9243	0.9044	0.9442	0.0000	0.0001	0.0101	9304
	Up to 2 y	46	0.9240	0.8996	0.9484	0.0000	0.0002	0.0125	5283
	Up to 12 mo	15	0.9074	0.8775	0.9372	0.0000	0.0002	0.0152	2664
	Up to 6 mo	2	0.9104	0.8862	0.9345	0.0000	0.0002	0.0123	292
	ANOVA Q test random effects with separate estimates of T ²				Sig = 0.678		Total patient samples		17,543
VAS back	More than 2 y	25	0.7075	0.6043	0.8106	0.0000	0.0028	0.0526	4948
	Up to 2 y	21	0.9023	0.8723	0.9323	0.0000	0.0002	0.0153	1978
	Up to 12 mo	6	0.7007	0.5910	0.8104	0.0000	0.0031	0.0560	872
	ANOVA Q est random effects with separate estimates of T ²				Sig <0.0001		Total patient samples		7798
VAS leg	More than 2 y	43	0.8920	0.8651	0.9190	0.0000	0.0002	0.0138	8690
	Up to 2 y	46	0.9441	0.9299	0.9582	0.0000	0.0001	0.0072	5237
	Up to 12 mo	16	0.8915	0.8465	0.9365	0.0000	0.0005	0.0230	2768
	Up to 6 mo	2	0.8366	0.8088	0.8643	0.0000	0.0002	0.0142	292
	ANOVA Q test random effects with separate estimates of T ²				Sig <0.0001		Total patient samples		16,987

ANOVA, analysis of variance; Sig, significance level of 95% CI; VAS, visual analog scale.