TABLE 3.
Characteristics of meta-analyses and analytic results1
| Meta-analyses (n = 115) | |
|---|---|
| Among reviews that used >1 method (i.e., model or type) of meta-analysis (n = 49; 42.6%), was the primary meta-analytic method explicitly defined? | |
| Yes | 1 (2.0) |
| No | 48 (98.0) |
| Primary model for meta-analysis | |
| Random-effects | 84 (73.0) |
| Fixed-effect | 1 (0.9) |
| Random-effects with significant or substantial heterogeneity, fixed-effect otherwise | 30 (26.1) |
| Primary type of meta-analysis | |
| Meta-analysis of extreme categories of intake | 87 (75.7) |
| Dose-response meta-analysis | 8 (7.0) |
| Meta-analysis of specific dose categories | 11 (9.6) |
| Other | 9 (7.8) |
| Secondary model for meta-analysis among reviews that used >1 method (i.e., model or type) for meta-analysis (n = 49; 42.6%) | |
| Random-effects | 36 (73.5) |
| Fixed-effect | 3 (6.1) |
| Random-effects with significant or substantial heterogeneity, fixed-effect otherwise | 10 (20.4) |
| Secondary type for meta-analysis among reviews that used >1 method (i.e., model or type) for meta-analysis (n = 49; 42.6%)2 | |
| Meta-analysis of extreme categories of intake | 3 (6.1) |
| Dose-response meta-analysis | 31 (63.3) |
| Meta-analysis of specific dose categories | 6 (12.2) |
| Other | 4 (8.2) |
| Among reviews that did not conduct dose-response meta-analysis (n = 67; 58.3%), was the decision to not conduct dose-response meta-analysis justified, either by the authors in the report or based on the question being investigated? | |
| Yes | 17 (25.4) |
| No | 50 (74.6) |
| Were any subgroup analyses reported? | |
| Yes | 103 (89.6) |
| No | 12 (10.4) |
| Subgroup analyses among reviews with subgroup analyses, n (n = 103, 89.6%) | 4 [2–7] |
| Among reviews with subgroup analyses (n = 103; 89.6%), were subgroup analyses prespecified? | |
| Yes, all subgroups were prespecified | 6 (5.8) |
| Yes, some were prespecified and others were post hoc | 8 (7.8) |
| No | 4 (3.9) |
| Not reported | 85 (82.5) |
| Study designs pooled in primary meta-analysis | |
| Cohorts | 32 (27.8) |
| Case-control | 5 (4.3) |
| Cross-sectional | 7 (6.1) |
| RCTs + cohorts | 1 (0.9) |
| RCTs + cohorts + case-control | 1 (0.9) |
| Cohorts + case-control | 30 (26.1) |
| Cohorts + cross-sectional | 9 (7.8) |
| Cohorts + case-control + cross-sectional | 13 (11.3) |
| Case-control + cross-sectional | 3 (2.6) |
| Not reported | 14 (12.2) |
| Among meta-analyses that included different study designs (n = 57; 49.6%), did the review present subgroup analyses by study design? | |
| Yes | 48 (84.2) |
| No | 9 (15.8) |
| Test for small study effects2 | |
| Egger's test | 82 (71.3) |
| Visual inspection of funnel plot | 72 (62.6) |
| Begg's test | 35 (30.4) |
| No test for small study effects | 15 (13.0) |
| Among meta-analyses that tested for small study effects (n = 100; 87.0%), was there evidence of small study effects? | |
| Yes | 38 (38.0) |
| No | 60 (60.0) |
| Not reported | 2 (2.0) |
| Among meta-analyses with evidence of small study effects (n = 38; 33.0%), were results adjusted for small study effects? | |
| Yes, using trim and fill (28) | 15 (39.5) |
| Yes, a study was excluded | 2 (5.3) |
| No | 21 (55.3) |
| Other analytic errors and suboptimal practices2 | |
| Misestimation of heterogeneity due to the pooling of stratified data in the main meta-analysis | 21 (18.3) |
| Double-counting of studies in meta-analyses | 20 (17.4) |
| Studies included in the primary meta-analysis, n | 10 [6–14] |
| Effect size of the primary meta-analysis among meta-analyses with dichotomous outcomes (n = 110; 95.6%)3 | |
| Very small or no effect (relative effect of 1.0–1.1) | 32 (29.0) |
| Small (relative effect of 1.1–1.5) | 68 (61.8) |
| Moderate (relative effect of 1.51–2.00) | 8 (7.3) |
| Large (relative effect > 2.01) | 2 (1.8) |
| Was the primary meta-analysis statistically significant? | |
| Yes | 79 (68.7) |
| No | 36 (31.3) |
| Magnitude of heterogeneity (I2) in the primary meta-analysis | |
| <25% | 23 (20) |
| 25 to <50% | 18 (15.7) |
| 50 to <75% | 43 (37.4) |
| 75% to 100% | 28 (24.3) |
| Not reported | 3 (2.6) |
1
Values are n (%) or median [IQR]. RCT, randomized controlled trial.
2
Each review can be classified in >1 category.
3
We converted effect estimates so that increasing levels of exposure were associated with increasing risk of the outcome.