Table 1 Study characteristics by aggregation level

Number of studies

12

11

99

98

95

30

Average cohort size

5.433

26.483

154.370

385.274

1.032.698

680.265

Median cohort size

5.559

2.841

23.236

74.074

259.627

133.293

Entire population measured (instead of sample)

100%

91%

79%

59%

64%

30%

Reported variation in caesarean section rate (average of studies)

8–36%

15–26%

13–37%

25–44%

15–34%

12–37%

Reported variation in caesarean section rate (median of studies)

6–35%

11–29%

11–33%

23–37%

15–30%

11–40%

Case-mix correction

4 (33%)

3 (27%)

42 (42%)

28 (29%)

22 (23%)

6 (20%)

Medical outcome

9 (75%)

5 (45%)

24 (24%)

11 (11%)

12 (13%)

7 (23%)