for the main comparison.

Any type of transcutaneous electrostimulation compared with sham or no intervention for osteoarthritis of the knee
Patient or population: patients with osteoarthritis Settings: physical therapy practice of outpatient clinic Intervention: any type of transcutaneous applied electrostimulation Comparison: sham or no specific intervention
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk*	Corresponding risk
	Sham or no specific intervention	Any type of transcutaneous electrostimulation
Pain Various pain scales Median follow‐up: 4 weeks	‐1.8 cm change on 10 cm VAS1 29% improvement	‐2.0 cm change (Δ ‐0.2 cm, ‐1.2 to 0.8 cm)2 33% improvement (Δ +4%, ‐13% to +20%)3	SMD ‐0.07 (‐0.46 to 0.32)	726 (16 studies)	+OOO very low4	Little evidence of beneficial effect (NNT: not statistically significant) The estimated pain in the intervention group of large trials was derived from meta‐regression using the standard error as independent variable
Function Various validated function scales Median follow‐up: 4 weeks	‐1.2 units on WOMAC (range 0 to 10)1 21% improvement	‐2.3 units on WOMAC (Δ ‐1.1, ‐1.6 to ‐0.6)5 41% improvement (Δ +20%, +11% to +29%)6	SMD ‐0.34 (‐0.54 to ‐0.14)	407 (9 studies)	+OOO very low7	NNT: 10 (95% CI 7 to 22)8
Number of patients experiencing any adverse event Median follow‐up: 4 weeks	150 per 1000 patient‐years1	153 per 1000 patient‐years (80 to 296)	RR 1.02 (0.53 to 1.97)	175 (3 studies)	++OO low9	No evidence of harmful effect (NNH: not statistically significant)
Number of patients withdrawn or dropped out because of adverse events Median follow‐up: 4 weeks	17 per 1000 patient‐years1	16 per 1000 patient‐years (3 to 102)	RR 0.97 (0.16 to 6.00)	363 (8 studies)	+++O moderate10	No evidence of harmful effect (NNH: not statistically significant)
Number of patients experiencing any serious adverse event Median follow ‐up: 4 weeks	4 per 1000 patient‐years1	1 per 1000 patient‐years (0 to 29)	RR 0.33 (0.02 to 7.32)	195 (4 studies)	++OO low11	No evidence of harmful effect (NNH: not statistically significant)
*The basis for the assumed risk in the safety outcomes (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; GRADE: GRADE Working Group grades of evidence (see explanations); NNT: number needed to treat; NNH: number needed to harm; RR: risk ratio; SMD: standardised mean difference

GRADE Working Group grades of evidence 
 High quality (++++): Further research is very unlikely to change our confidence in the estimate of effect. 
 Moderate quality (+++O): Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. 
 Low quality (++OO): Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. 
 Very low quality (+OOO): We are very uncertain about the estimate.

¹ Median reduction as observed across control groups in large osteoarthritis trials (Nuesch 2009). 
 ² Standardised mean differences (SMDs) were back‐transformed onto a 10 cm visual analogue scale (VAS) on the basis of a typical pooled SD of 2.5 cm in trials that assessed 
 pain using a VAS, and expressed as change based on an assumed standardised reduction of 0.72 standard deviation units in the control group. 
 ³ The median observed pain score at baseline across control groups in large osteoarthritis trials was 6.1 cm on a 10 cm VAS (Nuesch 2009). 
 ⁴ Downgraded (3 levels) because the effect was estimated from a meta‐regression model using the standard error as independent variable and because included trials were generally of low quality and small sample size: only 2 out of 16 trials used adequate concealment of allocation, only 3 performed analyses according to the intention‐to‐treat principle, and the presence of large between trial heterogeneity. 
 ⁵ Standardised mean differences (SMDs) were back‐transformed onto a 0 to 10 standardised WOMAC function score on the basis of a typical pooled SD of 2.1 in trials that 
 assessed function on WOMAC function scale and expressed as change based on an assumed standardised reduction of 0.58 standard deviation units in the control group. 
 ⁶ The median observed standardised WOMAC function score at baseline across control groups in large osteoarthritis trials was 5.6 units (Nuesch 2009). 
 ⁷ Downgraded (3 levels) because included trials were generally of low quality and small sample size: 1 out of 9 studies used adequate concealment of allocation methods, only 2 performed analyses according to the intention‐to‐treat principle, presence of moderate between trial heterogeneity, 9 out of 18 studies reported this outcome, likely leading to selective outcome reporting bias. 
 ⁸ Absolute response risks for function in the control groups were assumed 26% (see Methods section). 
 ⁹ Downgraded (2 levels) because the confidence interval crosses no difference in the pooled estimate, 1 out of 3 studies included all patients in this analysis, 3 out of 18 studies reported this outcome, likely leading to selective outcome reporting bias. 
 ¹⁰ Downgraded (1 level) because the confidence interval of the pooled estimate is wide and crossed no difference, 8 out of 18 studies reported this outcome, possibly leading to selective outcome reporting bias. 
 ¹¹ Downgraded (2 levels) because 4 out of 18 studies reported this outcome, possibly leading to selective outcome reporting bias, the confidence interval of the pooled estimate is wide and crossed no difference.