Summary of findings 3.

Transcranial direct current stimulation (tDCS) compared with sham for chronic pain

tDCS compared with sham for chronic pain
Patient or population: adults with chronic pain Settings: laboratory/ clinic Intervention: active tDCS Comparison: sham tDCS
Outcomes	Effect size	Relative effect (average % improvement (reduction) in pain (95% CIs) in relation to post‐treatment score from sham group)* *Where 95%CIs do not cross the line of no effect.	No of participants (studies)	Quality of the evidence (GRADE)
Pain intensity (0 to < 1 week postintervention) measured using visual analogue scales or numerical rating scales	SMD ‐0.43 (‐0.63 to ‐0.22)	This equates to a 17% (95% CI 9% to 25%) reduction in pain intensity or a 0.82 (95% CI 0.42 to 1.2) point reduction on a 0 to 10 pain intensity scale.	747 (27)	⊕⊝⊝⊝ very low1
Disability (0 to < 1 week postintervention) measured using self‐reported disability/pain interference scales	SMD ‐0.01, (95% CI ‐0.28 to 0.26)	‐	212 (4)	⊕⊕⊝⊝ low2
Quality of life (0 to < 1 week postintervention) measured using different scales across studies	SMD 0.66, 95% CI 0.21 to 1.11	‐	82 (4)	⊕⊕⊝⊝ low2
CI: confidence interval; MD: mean difference; SMD: standardised mean difference; tDCS: transcranial direct current stimulation
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect; Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different; Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect; Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

¹Downgraded once for study limitations due to high or unclear risk of bias, once for inconsistency due to heterogeneity and once for evidence of possible publication bias. ²Downgraded once for study limitations due to high or unclear risk of bias and once for imprecision due to low participant numbers.