Invited commentary: Epidemiologic studies of the health associations of environmental exposures with preterm birth.

In this issue of the Journal, two different articles present epidemiologic evidence supporting the hypotheses that environmental exposures to particulate air pollution or higher temperatures modestly increase the risk of preterm birth. In this commentary, the author discusses environmental epidemiologic methods through the lens of these two papers with respect to the causal question, measurements, and quantification and interpretation of the evidence. Both groups of investigators present results from exploratory analyses that are at the hypothesis-generating end of the research spectrum as opposed to the confirmatory end. The present author describes in qualitative terms a method for decomposing evidence about the association of environmental exposures with prematurity into components representing different temporal and spatial scales. Finally, reproducible epidemiologic research methodology for studies like these is offered as one way to speed the transition from exploratory studies to confirmatory studies.