Assessment of recent ozone short-term epidemiologic studies

The U.S. Environmental Protection Agency (EPA) revised the National Ambient Air Quality Standards (NAAQS) for ozone in 1997 based largely on short-term ozone studies published up to 1995. The U.S. EPA's conclusions must now be updated because (1) the agency did not consider many new studies published since 1995 and (2) the agency did not critically review the studies published before 1995 (i.e., it accepted the stated conclusions). In this article, we examine many recently published short-term ozone studies including 17 hospital admissions studies, 10 mortality studies, and 6 summer-camp studies. Almost all of these studies reported a significant association between ambient levels of ozone and adverse health effects. However, on close examination, it is apparent that there are mixed findings from one study to another and even within the results of a single study. Moreover, questionable statistical analyses and failure to consider confounders make a number of the reported findings doubtful and even negative.