Table 2. Outcome scores broken up by follow-up period with standardized difference of means reflecting standardized treatment effect.

Questionnaire	Follow up	N	Mean ± SD	MD (postop. mean – preop. mean)	|SMD|=|MD/SDpreop.|	P value
VAS (0–10)	Preop.	57	6.2±1.8	n/a	n/a	n/a
	12-month	39	3.9±3.2	−2.3	1.3†	<0.001
	13–22 months	13	2.8±2.8	−3.4	1.9†	<0.001
ODI	Preop.	32	49.2±16.0	n/a	n/a	n/a
	12-month	13	24.6±12.9	−24.6	1.5†	0.04
	13–22 months	17	20.8±19.5	−28.4	1.8†	0.01
DSIJQ	Preop.	20	53.2±11.6	n/a	n/a	n/a
	12-month	10	17.4±17.2	−35.8	3.1†	0.06
	13–22 months	16	20.8±21.0	−32.4	2.8†	0.02

^†, an |SMD|, standardized mean difference in the absolute value, |SMD| >0.8 indicates a strong treatment effect. SD, standard deviation; MD, mean difference; VAS, Visual Analogue Scale; ODI, Oswestry Disability Index; DSIJQ, Denver Sacroiliac Joint Questionnaire.