Category | Summary of Criteria | Downgrades | Rationale |
Initial Rating of Human Evidence = “Moderate” | |||
Risk of Bias | Study limitations- a substantial risk of bias across body of evidence. | -1 | Downgraded because of “probably high” risk of bias for air pollution exposure assessment for four studies and for pollen exposure assessment for five studies. |
Indirectness | Evidence was not directly comparable to the chosen population, exposure, comparator, and outcome. | 0 | Measured outcomes were assessed for humans in populations for the duration of study periods, as outlined in the PECO statement. |
Inconsistency | Wide variability in estimates of effect in similar populations. | 0 | Some evidence of consistent effects, but the studies were too varied in definitions of risk factors and methods to judge consistency in effect estimates. |
Imprecision | Studies had a small sample size and small outcome count. | 0 | The studies had large sample sizes with adequate samples for outcomes during study periods. |
Publication Bias | Studies missing for body of evidence, resulting in an over or underestimate of true effects from exposure. | 0 | The studies were large studies that varied in year, data sources, and methods of statistical analysis that appeared to report outcomes found regardless of results. |
Category | Summary of Criteria | Upgrades | Rationale |
Large magnitude of effects | Study found confounding alone unlikely to explain association with large effect estimate as judged by reviewers. | 0 | Studies that reported positive associations of interactions reported effect estimates with low magnitudes. |
Dose-response | Consistent relationship between dose and response in one or multiple studies, and/or exposure response across studies. | 0 | Studies did not report a consistent relationship between dose and response. |
Confounding minimizes effect | Upgraded if consideration of all plausible residual confounders or biases would underestimate the effect or suggest a spurious effect when results show no effect. | 0 | No evidence that residual confounders or biases would underestimate the effect or suggest a spurious effect when results show no effect. |
Overall Quality of Evidence | Low | The overall quality of the evidence supporting interactive effects is low. | |
Overall Strength of Evidence | Limited | An association was sometimes observed for synergy between heat, air pollution, and pollen, but the potentially high risk of bias for air pollution exposure could have impacted results and there is a lack of consistently significant findings. |