Invited commentary: Considering bias in the assessment of respiratory symptoms among residents of Lower Manhattan following the events of September 11, 2001.

The report by Lin et al. (1) in this issue of the Journal presents data on past-year and past-month respiratory symptoms among residents of Lower Manhattan after the September 11, 2001, attack on and collapse of the World Trade Center, as compared with residents of Manhattan’s Upper West Side. Residents of both areas were surveyed 8–16 months after the attack. The recorded frequency of symptoms after September 11 was higher in the exposed area than in the unexposed (or less exposed) area. The pervasiveness of the smoke, dust, and debris that permeated parts of Lower Manhattan for months after the September 11 attacks makes the respiratory tract irritation and symptoms reported by the residents in this study entirely plausible. While respiratory irritation and symptoms have been described in firefighters who were heavily exposed during these events (2), this study is noteworthy and laudable for its attempt to focus on the general population. However, this study in some ways raises more questions than it answers. In particular, key questions about potential bias, assessment of exposure and health outcomes, and potential unmeasured confounding pose considerable challenges to the interpretation of the results documented here.