1. Results of stratified analyses of pain outcomes.
| Variable | N of trials | N of patients (experimental) | N of patients (control) | Pain intensity | Heterogeneity | P for interaction |
| n | n | n | SMD (95% CI) | I2 (%) | ||
| All trials | 16 | 440 | 286 | ‐0.86 (‐1.23 to ‐0.49) | 80% | |
| Allocation concealment | 0.47 | |||||
| Adequate | 2 | 79 | 39 | ‐0.52 (‐0.91 to ‐0.13) | 0% | |
| Inadequate or unclear | 14 | 361 | 247 | ‐1.03 (‐1.49 to ‐0.57) | 84% | |
| Type of control intervention* | 0.12 | |||||
| Sham intervention | 12 | 354 | 216 | ‐1.13 (‐1.59 to ‐0.67) | 82% | |
| No control intervention | 5 | 86 | 70 | ‐0.31 (‐0.80 to 0.19) | 58% | |
| Blinding of patients | 0.37 | |||||
| Adequate | 11 | 309 | 205 | ‐1.05 (‐1.52 to ‐0.59) | 82% | |
| Inadequate or unclear | 6 | 131 | 79 | ‐0.63 (‐1.31 to 0.05) | 81% | |
| Use of analgesic cointerventions | 0.36 | |||||
| Similar between groups | 4 | 124 | 83 | ‐0.57 (‐1.16 to 0.02) | 74% | |
| Not similar or unclear | 12 | 316 | 23 | ‐1.10 (‐1.60 to ‐0.59) | 84% | |
| Intention‐to‐treat analysis | 0.73 | |||||
| Yes | 3 | 83 | 63 | ‐0.76 (‐1.43 to ‐0.09) | 72% | |
| No or unclear | 13 | 357 | 223 | ‐1.00 (‐1.48 to ‐0.53) | 84% | |
| Type of ES** | 0.94 | |||||
| High frequency TENS | 8 | 177 | 139 | ‐0.82 (‐1.51 to ‐0.12) | 86% | |
| Burst TENS | 2 | 39 | 38 | ‐0.85 (‐1.32 to ‐0.38) | 0% | |
| Modulation TENS | 1 | 13 | 3 | ‐1.41 (‐2.92 to 0.10) | N/A | |
| Low frequency TENS | 3 | 46 | 40 | ‐0.82 (‐1.29 to ‐0.34) | 0% | |
| Interferential current stimulation | 4 | 88 | 44 | ‐1.20 (‐1.99 to ‐0.42) | 71% | |
| Pulsed ES | 2 | 77 | 52 | ‐0.41 (‐0.77 to ‐0.05) | 0% | |
| Duration of ES per session† | 0.69‡ | |||||
| ≤ 20 minutes | 8 | 166 | 112 | ‐0.95 (‐1.55 to ‐0.35) | 78% | |
| 30 to 40 minutes | 6 | 156 | 99 | ‐1.45 (‐2.28 to ‐0.62) | 85% | |
| ≥ 60 minutes | 4 | 118 | 91 | ‐0.47 (‐0.96 to 0.02) | 58% | |
| Number of sessions per week | 0.90‡ | |||||
| ≤ 3 | 6 | 163 | 91 | ‐0.81 (‐1.48 to ‐0.14) | 82% | |
| 4 to 6 | 7 | 182 | 125 | ‐1.33 (‐2.11 to ‐0.54) | 88% | |
| ≥ 7 | 3 | 96 | 70 | ‐0.51 (‐0.83 to ‐0.19) | 0% | |
| Duration of ES per week*** | 0.74‡ | |||||
| ≤1 hour | 5 | 123 | 71 | ‐0.85 (‐1.72 to 0.01) | 86% | |
| > 1 to 5 hours | 8 | 180 | 122 | ‐1.42 (‐2.11 to ‐0.74) | 81% | |
| > 5 hours | 5 | 137 | 109 | ‐0.53 (‐0.96 to ‐0.11) | 55% | |
| Duration of treatment period | 0.14 | |||||
| < 4 weeks | 7 | 190 | 114 | ‐1.39 (‐2.13 to ‐0.66) | 86% | |
| ≥ 4 weeks | 9 | 250 | 172 | ‐0.64 (‐1.06 to ‐0.22) | 75% |
ES: electrostimulation; *In Cheing 2002, two independent comparisons contributed in the two different strata. **Adedoyin 2005, Grimmer 1992 and Law 2004 contributed to two, two and three different strata: high‐frequency TENS and interferential current stimulation, high‐frequency TENS and burst, and high‐, low‐frequency and modulation TENS, respectively. † = Cheing 2003 contributed to all three different strata, with the same 8 control patients displayed in each stratum. ‡ = P values from test for trend.