] in assessing the body of evidence for demonstrating the health effects of exposures. The body of evidence for inferring causation is populated by contributions derived and made available from different epidemiological approaches. These contributions range from the less informative case studies to descriptive analyses comparing observed to expected numbers of illness events across exposed and unexposed groups of people.
Given the above hierarchy of epidemiological studies, to further address question of causation, appropriately designed observational studies would be utilised instead of RCTs because it would not be ethical to undertake RCTs, exposing people to toxic fumes. The most informative of the available observational epidemiological study designs is that of the prospective cohort study.
In terms of the evidence to date of health effects associated with contaminated aircraft and fume events, numerous case reports, case-series, and descriptive studies have been undertaken and they should not be ignored. Importantly, there has been an over-reliance on the lack of exposure data collected during fume events, despite there being no sensors to take measurements. This has been at the expense of failing to consider that the air supply and engine system designs enable exposure to oils to occur in both normal operations and abnormal conditions.