Gulf War and Health Volume 9: Long-Term Effects of Blast Exposures (2014) / Chapter Skim
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2 Methods
2 Methods
Pages 21-32
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From page 21... ...
SEARCH STRATEGY AND IDENTIFICATION OF LITERATURE To identify the relevant published evidence on health effects of blast exposure, the committee began its work by overseeing extensive searches of the medical and scientific literature, such as published peer-reviewed articles and technical reports. Citation databases searched included MEDLINE, Embase, and the National Technical Information Service.
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From page 22... ...
TYPES OF EVIDENCE The committee relied primarily on clinical and epidemiologic studies to draw its conclusions about the strength of evidence of associations between blast exposures and long-term health effects. However, animal studies played a critical role in clarifying the mechanism of blast injuries and provided biologic understanding of many of the effects seen in humans.
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From page 23... ...
-- is associated with both the exposure and the outcome and leads to the mistaken conclusion that the exposure is associated with the outcome. Effect–cause relationships occur when the outcome precedes the exposure; for example, a study might suggest that a particular health outcome was associated with blast exposure when the health condition actually preceded the exposure.
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From page 24... ...
In deciding on associations between blast exposure and human longterm health effects, the committee used evidence only from human studies; in some cases, however, it examined animal studies as a basis of judgments about biologic mechanism or plausibility. INFERRING CAUSALITY Determining whether a given statistical association rises to the level of causation requires inference (Hill, 1965)
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From page 25... ...
risk or ratio, an association that is found in a number of studies, an increased risk of disease with increasing exposure or a decline in risk after cessation of exposure, and a finding of the same outcome after analogous exposures all strengthen the likelihood that an association seen in epidemiologic studies is causal. Exposures are rarely, if ever, controlled in observational studies, and there can be substantial uncertainty in the assessment of a blast exposure.
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From page 26... ...
A primary study had to include an unexposed control or comparison group, had to have sufficient statistical power to detect effects, had to use reasonable methods to control for confounders, and had to report followup data for at least 6 months. A study had to include information that the exposure was to blast.
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From page 27... ...
For psychiatric outcomes, standardized interviews were preferred, such as the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, the Diagnostic Interview Schedule, and the Composite International Diagnostic Interview; similarly, for other outcomes, standardized and validated tests were preferred. The committee recognizes that not all health outcomes have objective measures (for example, tinnitus is identified only through self-reported symptoms)
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From page 28... ...
Sufficient Evidence of an Association Evidence is sufficient to conclude that there is a positive association; that is, a consistent association has been observed between blast exposure and a specific health outcome in human studies in which chance and bias, including confounding, could be ruled out with reasonable confidence as an explanation for the observed association.
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From page 29... ...
The committee reviewed the evidence on those immediate, permanent injuries but, given its charge, focused on long-term consequences of injuries to the body from blast exposures. Service members can sustain injuries from which they seemingly recover but that initiate a constellation of adverse consequences that are not clinically obvious shortly after exposure to blast, being revealed only later, as depicted by the trajectories in Panel C
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From page 30... ...
30 GULF WAR AND HEALTH A Acute Onset Worse Functioning Time Blast B Figure – Onset 1 Delayed Blast R02369 Gulf War Worse Functioning Time Blast Figure – Blast 2 R02369 Gulf War
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From page 31... ...
Service members who do not suffer apparent initial acute injury from blast exposures may be susceptible to long-term consequences (see Panel B)
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From page 32... ...
Few data on such interactive effects are available. A key question addressed by the committee later in this report is which long-term consequences can occur only as a result of clinically detectable acute injuries and which can occur even in the absence of clinically detectable acute injuries.
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