Table III. —Interpretation of the size of effect.

Parameter	Small effect	Moderate effect*	Large effect*
Standardized mean difference (SMD)	<0.3	0.3 to 0.5	>0.5
VAS/NPRS (0-10), MD	<1	1 to 2	>2
RMDQ (0-24), MD	<2	2 to 5	>5
ODI / QBPDS (0-100), MD	<10	10 to 20	>20
Quality of life (SF-12, SF 36, PCS 0-100), MD	<10	10 to 20	>20
Quality of life (SF-12, SF 36, MCS 0-100), MD	<10	10 to 20	>20

VAS: Visual Analogue Scale; NPRS: Numeric Pain Rating Scale; MD: mean difference; RMDQ: Roland Morris Disability Questionnaire; ODI: Oswestry Disability Index; QBPDS: Quebec Back Pain Disability Scale; SF-12: 12-items Short Form Health Survey; SF-36: 36-items Short Form Health Survey; PCS: physical component summary; MCS: mental component summary. *A moderate and large effect are also considered to be clinically relevant.