Skip to main content

Table 2 Overview of the main results for binary outcomes

From: Empirical evidence of study design biases in nutrition randomised controlled trials: a meta-epidemiological study

Methodological trial characteristic (high/unclear versus low RoB judgement)

N (meta-analyses)

RRR (95% CI)

Heterogeneity (I2; Ï„2)

95% PIa

Random sequence generation

 Main analysis

39

0.97 (0.93; 1.02)

28%; 0.002

0.88; 1.08

 Micronutrients

23

0.96 (0.92; 1.00)

2%; 0

0.91; 1.00

 Fatty acids

11

0.97 (0.76; 1.23)

62%; 0.09

0.76; 1.23

 Dietary approach

3

0.99 (0.82; 1.20)

0%; 0

0.29; 3.41

 All-cause mortality

11

0.96 (0.88; 1.04)

19%; 0.005

0.80; 1.16

 Pregnancy outcomes

7

0.98 (0.90; 1.07)

38%; 0

0.88; 1.10

 Mostly subjectively assessed

21

1.00 (0.87; 1.14)

35%; 0.03

0.69; 1.44

 Excluding highly correlated outcomes

28

0.94 (0.85; 1.03)

42%; 0.02

0.69; 1.26

 Including only one outcome per comparison

19

0.98 (0.92; 1.04)

28%; 0.003

0.85; 1,12

Allocation concealment

 Main analysis

46

1.00 (0.96; 1.04)

27%; 0.001

0.92; 1.08

 Micronutrients

26

1.00 (0.95; 1.06)

33%; 0.002

0.90; 1.11

 Fatty acids

14

0.93 (0.83; 1.05)

37%; 0.01

0.70; 1.25

 Dietary approach

4

1.05 (0.96; 1.15)

0%; 0

0.85; 1.29

 All-cause mortality

12

0.97 (0.91; 1.04)

33%; 0.003

0.85; 1.12

 Pregnancy outcomes

11

1.04 (0.97; 1.11)

47%; 0

0.96; 1.12

 Mostly subjectively assessed

23

1.00 (0.92; 1.09)

13%; 0

0.92; 1.09

 Excluding highly correlated outcomes

34

0.98 (0.93; 1.03)

29%; 0.002

0.87; 1.09

 Including only one outcome per comparison

22

0.98 (0.93; 1.04)

25%; 0.002

0.88; 1.09

Blinding of participants and personnel

 Main analysis

29

0.95 (0.91; 1.00)

23%; 0

0.90; 1.01

 Micronutrients

17

0.95 (0.85; 1.07)

31%; 0.004

0.79; 1.15

 Fatty acids

11

0.96 (0.90; 1.02)

6%; 0

0.89; 1.03

 Dietary approach

n/a

n/a

n/a

n/a

 All-cause mortality

5

0.95 (0.87; 1.04)

0%; 0

0.83; 1.10

 Pregnancy outcomes

8

0.84 (0.59; 1.20)

59%; 0.14

0.30; 2.33

 Mostly subjectively assessed

16

0.94 (0.88; 1.01)

10%; 0

0.88; 1.02

 Excluding highly correlated outcomes

18

0.95 (0.89; 1.02)

6%; 0

0.88; 1.02

 Including only one outcome per comparison

11

0.96 (0.89; 1.04)

28%; < 0.0001

0.88; 1.05

Blinding of outcome assessment

 Main analysis

28

0.81 (0.70; 0.94)

26%; 0.03

0.54; 1.23

 Micronutrients

15

0.90 (0.77; 1.05)

37%; 0.02

0.62; 1.29

 Fatty acids

10

0.62 (0.47; 0.82)

0%; 0

0.45; 0.86

 Dietary approach

2

0.88 (0.39; 2.02)

0%; 0

n/a

 All-cause mortality

5

0.83 (0.64; 1.08)

0%; 0.02

0.46; 1.51

 Pregnancy outcomes

10

0.86 (0.62; 1.18)

49%; 0.11

0.37; 1.98

 Mostly subjectively assessed

13

0.74 (0.59; 0.93)

0%; 0.02

0.48; 1.13

 Excluding highly correlated outcomes

19

0.81 (0.67; 0.98)

27%; 0.04

0.51; 1.29

 Including only one outcome per comparison

12

0.88 (0.73; 1.07)

17%; 0.03

0.58; 1.35

Incomplete outcome data

 Main analysis

37

0.92 (0.88; 0.97)

22%; 0.001

0.85; 1.00

 Micronutrients

20

0.92 (0.87; 0.98)

36%; 0.001

0.85; 1.01

 Fatty acids

11

0.82 (0.72; 0.94)

0%; 0

0.71; 0.96

 Dietary approach

6

1.00 (0.89; 1.12)

42%; 0.001

0.83; 1.20

 All-cause mortality

11

0.91 (0.85: 0.98)

0%; 0

0.84; 0.99

 Pregnancy outcomes

11

0.76 (0.54; 1.07)

60%; 0.18

0.27; 2.14

 Mostly subjectively assessed

15

0.88 (0.78; 1.00)

0%; 0.01

0.69; 1.12

 Excluding highly correlated outcomes

26

0.93 (0.88; 0.99)

19%; 0.001

0.84; 1.03

 Including only one outcome per comparison

17

0.92 (0.86; 0.98)

38%; 0.002

0.82; 1.03

Selective reporting

 Main analysis

23

0.97 (0.92; 1.02)

24%; 0

0.92; 1.02

 Micronutrients

15

0.99 (0.92; 1.07)

19%; 0

0.92; 1.07

 Fatty acids

5

0.95 (0.89; 1.02)

63%; 0

0.86; 1.06

 Dietary approach

3

1.14 (0.54; 2.41)

0%; 0

0.01; 144.53

 All-cause mortality

7

0.96 (0.90; 1.02)

51%; < 0.0001

0.88; 1.04

 Pregnancy outcomes

8

0.99 (0.65; 1.51)

0%; 0

0.59; 1.68

 Mostly subjectively assessed

8

1.05 (0.90; 1.22)

48%; 0.02

0.70; 1.56

 Excluding highly correlated outcomes

18

0.98 (0.93; 1.04)

35%; 0

0.92; 1.04

 Including only one outcome per comparison

12

1.00 (0.81; 1.25)

56%; 0.07

0.54; 1.87

Dietary compliance

 Main analysis

15

0.95 (0.89; 1.02)

0%; 0

0.88; 1.03

 All-cause mortality

5

0.95 (0.86; 1.05)

0%; 0

0.81; 1.12

 Mostly subjectively assessed

10

0.96 (0.87; 1.06)

0%; 0

0.85; 1.08

 Excluding highly correlated outcomes

10

0.94 (0.87; 1.03)

0%; 0

0.85; 1.04

 Including only one outcome per comparison

6

0.99 (0.89; 1.09)

0%; < 0.0001

0.86; 1.13

  1. CI Confidence interval using z-critical value, I2 Heterogeneity measure, n/a Not applicable, PI Prediction interval using t-critical value, RoB Risk of bias, RRR Ratio of risk ratios, Ï„2 Heterogeneity value with the restricted maximum-likelihood estimation method
  2. aFor results with no heterogeneity (both I2 and τ2 = 0), the 95% PI may differ from the corresponding 95% CI, since calculations from 95% CIs are based on z-critical values, while calculations for 95% PIs are based on t-critical values