Table 1 Results of meta-analysis set 1

Studies (k)

19

5

20

13 included in [10]

2 included in [10]

13 included in [10]

1 excluded from [10]

3 new studies

1 excluded from [10]

5 new studies

6 new studies

Individuals in total (n)

189,422

Individuals per comparison (n)

188,922

39,123

189,274

Twins (n)

49,881

26,625

50,066

Singletons (n)

139,041

12,498

139,208

Prevalence in twins

9.13% (n = 4552)

3.39% (n = 903)

11.11% (n = 5564)

Prevalence in singletons

6.97% (n = 9692)

2.67% (n = 334)

7.23% (n = 10,069)

OR [95% CI]

1.40 [1.26, 1.57]

1.08 [0.52, 2.27]

1.36 [1.22, 1.52]

z

5.98***

0.21

5.65***

Heterogeneity among studies

Q(18) = 45.42***

Q(4) = 10.39*

Q(19) = 37.94**

I² = 60.39%

I² = 72.68%

I² = 61.06%

Tau² = 0.02

Tau² = 0.46

Tau² = 0.02