Luedtke 2015

Methods	Parallel RCT
Participants	Country of study: Germany Setting: back pain clinic Condition: chronic nonspecific low back pain Prior management details: excluded if had spinal surgery in previous 6 months n = 135 Age range: 26‐64 years, mean (SD) active group 45(9), sham group 44 (10) Duration of symptoms, mean (SD) active group 45 (9) months, sham group 44 (10) Gender distribution: 63 F, 72 M
Interventions	Stimulation type: tDCS Stimulation parameters: intensity 2 mA, 35 cm2 electrodes, duration 20 min Stimulation location: anode L M1, cathode right supraorbital area Number of treatments: x1 daIly for 5 d Control type: sham tDCS
Outcomes	Primary: pain VAS anchors not reported When taken: end of intervention, 4, 12 and 24 weeks postintervention Secondary: Oswestry Disability Index
Notes	Sources of support: "This study was funded by the Deutsche Forschungsgemeinschaft DFG (MA 1862/10‐1)." Competing interests: "AM, TJ, KL, and AP had financial support from DFG (MA 1862/10‐1) and NeuroImageNord for the submitted work."
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: “We randomised 160 stimulation codes (80 triggering active stimulation, 80 triggering sham stimulation) by custom written software into two separate lists.”
Allocation concealment (selection bias)	Low risk	Quote: “An independent researcher created the randomisation lists. To achieve allocation concealment the recruiter provided participants with the next unused stimulation code from the randomised lists. The recruiter had no access to the randomisation list.”
Adequate blinding of participants?	Low risk	Quote: “Blinding of participants and the treating physiotherapist was achieved by using a sham paradigm identical to the anodal stimulation procedure…. “ kappa agreement ‐0.120. Comment While 2 mA intensity can be inadequately blinded, assessment suggests blinding successful
Adequate blinding of assessors?	Low risk	Comment: while 2 mA intensity can be inadequately blinded, formal assessment suggests blinding successful
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: only 3 in each group discontinued in stimulation period. ITT approach
Selective reporting (reporting bias)	Low risk	Comment: reporting of all core outcomes
Study Size	Unclear risk	Comment: n = 67 and 68 per group
Study duration	Low risk	Comment: 24‐week follow‐up
Other bias	Low risk	Comment: no other bias detected