Evidence Consistency via a Study Quality Lens in Systematic Reviews: a case-study of formaldehyde exposure and respiratory associations abstract

Background/Aim: The evidence on exposure – health associations for chemicals with an extensive research history often includes studies with heterogeneous results. These studies may include various study designs examining different outcome and exposure definitions, and may be influenced to varying degrees by sources of bias and other factors that affect the magnitude, direction, and precision of effect estimates. Methods: We analyzed the impact of selected sources of bias and other quality criteria that could influence our confidence in the associations from studies of indoor formaldehyde exposure. The literature search (through February 2018) was based on population, exposure, comparator and outcome (PECO) criteria that included studies of children or adults exposed to formaldehyde in residential and occupational settings that analyzed associations with current asthma or reduced pulmonary function. Potential bias and other aspects of study quality were evaluated using a set of a priori criteria. Consistency was examined via forest plots stratifying by population, exposure (low vs high), overall study confidence and specific domain ratings. Results: A total of 32 population-based and occupational studies were identified. While there was considerable heterogeneity in the effect estimates as a whole for specific outcomes, stratifying by exposure level and setting, and overall confidence in the exposure-outcome association, indicated greater consistency within strata. Generally, multiple bias and quality domains contributed to the lower confidence ratings for individual study results potentially with opposing influence on the direction of bias, but stratification by domains clarified some of the greater heterogeneity observed among these exposure-outcome associations. Conclusions: While the specific determinants may vary, study quality considerations are essential to analyses of evidence consistency as part of the integration of evidence in systematic reviews. The views expressed in this abstract are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency.

Impact/Purpose

The evidence on exposure – health associations for chemicals with an extensive research history often includes studies with heterogeneous results, which may be influenced to varying degrees by sources of bias and other factors that affect the magnitude, direction, and precision of effect estimates. We analyzed the impact of selected sources of bias and other quality criteria that could influence our confidence in associations using a set of studies of indoor formaldehyde exposure as a case example. This presentation illustrates the importance of incorporating the results of study evaluations of bias and other factors during evidence integration to appropriately identify environmental hazards.

Citation

Glenn, B. AND E. RadkeFarabaugh. Evidence Consistency via a Study Quality Lens in Systematic Reviews: a case-study of formaldehyde exposure and respiratory associations abstract. International Society for Environmental Epidemiology annual meeting, Utrecht, NETHERLANDS, August 25 - 28, 2019.