Table 2 Meta-analysis of the subgroups of the included studies

Type of Study

 RCT

9

-1.70 (-2.97, -0.42)

< 0.001

 Crossover study

2

-1.55 (-2.10, -0.99)

0.48

Test of group differences: Q_b (1) = 0.04, p = 0.83

 Pain assessment tool

  VAS

7

-1.97 (-3.53, -0.41)

< 0.001

  NRS

4

-1.18 (-2.11, -0.25)

< 0.001

Test of group differences: Q_b (1) = 0.73, p = 0.39

 Number of tDCS sessions

  10 sessions

4

-2.87 (-5.29, -2.88)

< 0.001

  8 sessions

2

-1.67 (-2.35, -0.98)

0.16

  5 sessions

4

-0.43 (-1.59, 0.74)

< 0.001

  1 session

2

-0.74 (-2.69, 1.20)

< 0.001

Test of group differences: Q_b (3) = 5.22, p = 0.16

 Current intensity

  2 mA

8

-1.55 (-2.97, -0.13)

< 0.001

  Less than 2 mA

3

-1.88 (-2.67, -1.19)

0.18

Test of group differences: Q_b (1) = 0.17, p = 0.68

 Electrode Position

  M1

9

-1.13 (-2.75, 0.49)

< 0.001

  DLPFC

3

-4.19 (-9.01, 0.63)

< 0.001

Test of group differences: Qb (1) = 1.39, p = 0.24

 Sexuality

  Only Female

6

-1.29 (-2.68, 0.10)

< 0.001

  Female & Male

6

-1.71 (-3.35, -0.08)

< 0.001

Test of group differences: Q_b (1) = 0.15, p = 0.70