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2 Committee Approach
Pages 43-52

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From page 43...
... The committee systematically located, screened, and selected studies for review (including use of multiple databases to identify studies, predefined criteria to select studies for inclusion and exclusion, and systematically collecting data) ; evaluated individual studies for strengths and limitations; and synthesized findings into an assessment of the overall body of literature.
From page 44...
... LITERATURE REVIEW AND QUALITY ASSESSMENT Health Effects Literature For the assessment of studies on disease endpoints, in general, one committee member conducted an initial review of all literature identified pertaining to a set of outcomes. In its assessment of study strengths and limitations, the committee considered study design, elements of the design (e.g., sample size, setting, study population, exposure variables and methods of assessment, relevant controls or comparison groups, statistical methods, outcome measures assessed)
From page 45...
... The committee considered research design, conduct, analysis, and other sources of bias when assessing study strengths and weaknesses as it did for human studies. Smoking Transitions Literature The largest body of evidence was available on questions of e-cigarette use in relation to combustible tobacco cigarette smoking transitions (initiation and cessation)
From page 46...
... APPROACH TO ASSESSING CAUSALITY The committee faced some unique issues given the very recent introduction of e-cigarettes and limited empirical evidence for assessing their health effects. While there is a general consensus that high-quality epidemiological studies backed by solid toxicology and other mechanistic biological evidence provide the strongest basis for making firm inferences regarding causality, that simply does not exist for these devices.
From page 47...
... Conceptual Framework The committee developed a conceptual framework illustrating potential causal pathways by which e-cigarettes could affect health to help integrate and present evidence on known and likely e-cigarette exposures, potential mechanisms, intermediate outcomes, and disease endpoints. Figure 2-1 presents a simplified schematic of a generic plausible pathway between e-cigarettes and a health outcome.
From page 48...
... The committee considered data from humans to be most relevant for assessing human health risks of e-cigarettes, whereas additional animal data provide supporting evidence. For example, evidence of short-term effects of e-cigarette aerosol exposure from animal studies was considered weaker evidence compared with evidence of similar effects in humans.
From page 49...
... Establishing a temporal relationship, or that e-cigarette exposure occurred before the outcome was particularly relevant for effects on combustible tobacco cigarette smoking initiation, where reverse causation is plausible; temporality is less relevant for health effects because the likelihood that a disease endpoint or even an intermediate outcome would cause an individual to use cigarettes is unlikely. Establishing temporality is especially important in assessing observational data; longitudinal studies with multiple follow-up periods provide the strongest evidence of temporal precedence, whereas cross-sectional studies are considered weaker because they cannot exclude the possibility of reverse causation.
From page 50...
... Evidence of effects from animal and in vitro populations that were similar to and in the same direction as observed effects in human populations would be coherent with human studies. Therefore, if such research provided evidence of potential mechanisms or otherwise supporting biological plausibility, the committee considered it to bolster in vivo animal or epidemiological studies.
From page 51...
... Additional considerations regarding these factors specific to organ systems or smoking transitions are discussed in the relevant chapters of Sections II and III. CONCLUSIONS Informed by reports of previous Institute of Medicine and National Academies committees (IOM, 2011a, 2016; NASEM, 2017)
From page 52...
... 2015. Handbook for conducting a literature-based health assessment using OHAT approach for systematic review and evidence integration.


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