Dr. Ira Tager and colleagues at the University of California at Berkeley (UCB), and Dr. Patrick Kinney and colleagues at the School of Public Health, Columbia University objectives were to develop new methods for estimating an individual's past exposure to ozone. To estimate personal exposure to ozone, both groups of investigators combined historical data from a network of ozone monitoring sites (nationwide in Kinney's study, and California-based in Tager's) with data from questionnaires that obtained information about residence history, time spent outdoors, and level of activity while outdoors. Tager and coworkers studied UCB students who were lifetime residents of areas of California with either high or low levels of air pollution (the Los Angeles Basin or San Francisco Bay Area, respectively). In addition to estimating personal exposure to ozone, they also determined which tests of lung function, particularly small airway function, would be the most precise to use in a future, larger epidemiologic study. As part of his study, Tager then measured lung function in subjects whose long-term exposure to ozone he had previously estimated. Kinney studied Yale University students who had lived in different regions of the United States. He focused on evaluating the accuracy of different statistical methods for estimating previous ozone exposure, and in particular, on determining how many ozone monitoring sites were needed to provide data to make accurate estimates.