2. Materials and methods
2.1. Study design
Taking advantage of the changes in air pollution levels that occurred during the
2008 Beijing Olympic Games, we designed and conducted a panel study in which we enrolled a cohort of 201 participants residing in Beijing, China. We conducted in-person structured interviews with all subjects during their three clinic visits before (Baseline) and during (1st follow-up) and after (2nd follow-up) the Olympics that coincided with the changes in air pollution levels in Beijing.