To begin to assess the relative exposures, we made ambient air measurements and used recently developed methods for collecting exhaled breath in special containers.
Because of ongoing improvements in the methodology and because of the potential for monitoring population trends in exposure, we have made a particular effort to assure continuity, stability, and uniformity in our analyses over an extended time period.
The most influential sources of underestimation of the overall AF are likely to be (1) the choice of exposures we have made and (2) the existence of as yet unidentified workplace carcinogens.
Regarding the windows of exposure investigated, we made an effort to remain within the framework of the a priori hypothesis as stated, to the extent that acute windows of interest related to our literature review on pediatric asthma.
Given our lack of knowledge about the transmissibility of SARS at the time this exposure occurred, we made a conservative decision to quarantine for 10 days all persons who were in the unit for at least 4 h or who had a history of entry into the affected patient's room.
Because of the similar PM mass concentrations in each discrete exposure, we can make clear comparisons of PM attributes to their associated effects on allergic airways disease.
However, it is possible that the rapid decline in ETS exposure led us to underestimate the risks of CHD associated with ETS exposure, a point we made in our earlier paper [ 4], in which case the contribution of declining ETS exposure to the documented decline in CHD risk [ 22] may also have been underestimated.
Depending on the exposure variable under investigation, we made mutual adjustments for raw or processed fruit and vegetables.
In the main analyses of exposure and effect biomarkers, however, we made only a few comparisons, and the issue of chance findings due to multiple comparisons was minor.
There is evidence that the average of 2 days' pollution correlates better with mortality than a single day's exposure (Schwartz 2000), and therefore we made an a priori decision to study the average of lags 0 and 1 for CO.
