Table 1 Characteristics between placebo and untreated controls

	Placebo	Untreated control
	Placebo	Three-arm trials	Two-arm trials	All
No. of trials	193†	3	11	14
No. of patients	16 364	517	650	1167
Active treatments (no. of trials)	Various	Acupuncture (2) and magnetic (1)	Exercise (9), self-management (1) and knee tape (1)	Non-pharmacological
Quality of trials (%)
Randomisation	98	100	100	100
Blinding	93	NA	NA	NA
Intention to treat	31	67	36	43
Age, years	62.0 (4.7)	64.0 (1.3)	65.3 (3.2)*	65.0 (2.8)*
Gender, F/M	2.6 (1.9)	2.1 (0.1)	3.1 (1.3)	2.9 (1.2)
BMI, kg/m²	29.0 (2.6)	29.8	31.4 (2.0)*	31.1 (1.9)*
Baseline pain, %	54.9 (15.2)	43.9 (8.7)	41.3 (10.8)**	41.9 (10.2)**

Data given as mean (SD) unless otherwise indicated.
*p<0.05, **p<0.01 compared with placebo group; †193 placebo groups were available from 187 placebo controlled studies as 6 studies reported 2 separate placebo-controlled trials.
BMI, body mass index; F, female; M, male; NA, blinding was not applicable