Table 1. Summary of included items according to outcome, study design, and causality dimension.
| Congenital abnormalities | GBS | |||
|---|---|---|---|---|
| N | % | N | % | |
| Type of study | ||||
| Case report | 9 | 12.5 | 9 | 25 |
| Case series | 22 | 30.6 | 5 | 13.9 |
| Case-control study | 0 | 0 | 1 | 2.8 |
| Cohort study | 1 | 1.4 | 0 | 0 |
| Cross-sectional study | 2a | 2.8 | 0 | 0 |
| Ecological study/outbreak report | 5 | 6.9 | 19 | 52.8 |
| Modelling study | 2 | 2.8 | 0 | 0 |
| Animal experiment | 18 | 25 | 0 | 0 |
| In vitro experiment | 10 | 13.9 | 0 | 0 |
| Sequence analysis and phylogenetics | 3 | 4.2 | 2 | 5.6 |
| Total items | 72 | 100 | 36 | 100 |
| Causality dimensionb | ||||
| Temporality | 21 | 36.2 | 26 | 83.9 |
| Biological plausibility | 25 | 43.1 | 4 | 12.9 |
| Strength of association | 3 | 5.2 | 2 | 6.5 |
| Alternative explanation | 18 | 31 | 6 | 19.4 |
| Cessation | 2 | 3.4 | 6 | 19.4 |
| Dose–response relationship | 0 | 0 | 0 | 0 |
| Experiment | 20 | 34.5 | 0 | 0 |
| Analogy | NA | NA | NA | NA |
| Specificity | 0 | 0 | 0 | 0 |
| Consistency | NA | NA | NA | NA |
| Total groupsc | 58 | 31 | ||
a One cross-sectional study studied human participants and one studied monkeys.
b A group of items could contribute to more than one causality dimension, so totals do not sum to 100%.
c Two items contribute to both topics.
Abbreviations: NA, not applicable; evidence about analogous conditions was not searched systematically; the dimension of consistency used information in items included for all other causality dimensions.