the observed association. Accordingly, the criteria for each category express a degree of confidence based on the extent to which sources of error were reduced. The committee discussed the evidence and reached consensus on the categorization of that evidence for each health and psychosocial effect in Chapters 6 and 7, respectively. The committee was conservative in its judgment of the evidence as the quantity and quality of studies used for the determination of association for each health effect varied considerably, but in each case, the minimum requirements for the specific category of association were met.

Sufficient Evidence of a Causal Relationship

Evidence is sufficient to conclude that there is a causal relationship between exposure to deployment-related stress and a specific health effect in humans, and the evidence is supported by experimental data on humans or animals. The evidence fulfills the guidelines for sufficient evidence of an association (below) and satisfies several of the guidelines used to assess causality: strength of association, dose-response relationship, consistency of association, and a temporal relationship.

Sufficient Evidence of an Association

Evidence is sufficient to conclude that there is an association; that is, a consistent association has been observed between exposure to deployment-related stress and a specific health effect in human studies in which chance and bias, including confounding, could be ruled out with reasonable confidence as an explanation for the observed association. For example, several high-quality studies report consistent associations, and the studies are sufficiently free of bias, including adequate control for confounding.

Limited but Suggestive Evidence of an Association

Evidence is suggestive of an association between exposure to deployment-related stress and a specific health effect in human studies, but the body of evidence is limited by the inability to rule out chance and bias, including confounding, with confidence. At least one high-quality3 study reports a positive association that is sufficiently free of bias, including adequate control for confounding, and corroborating studies provide support for the association but are not sufficiently free of bias, including confounding. Alternatively, several studies of lower quality might show a consistent association with results that are probably not due to bias, including confounding.4

Inadequate/Insufficient Evidence to Determine Whether an Association Exists

Evidence is of insufficient quantity, quality, or consistency to permit a conclusion regarding the existence of an association between exposure to a specific agent and a specific health effect in humans.

3

Factors used to characterize high-quality studies include the statistical stability of the association, whether a dose-response relationship or other trend was demonstrated, and the quality of the assessments of exposure and effect.

4

Factors used to make this judgment include the data on the relationship between potential confounders and related health effects in a given study, information on subject selection, and classification of exposure.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement