Computational and methodological concerns in the GAM implementation for time series anal- yses of pollution and health delayed the review of the National Ambient Air Quality Standard (NAAQS) for PM, as the time series ¯ndings were a critical component of the evidence. The EPA deemed it necessary to re-evaluate all of the time series analyses that used GAM and were key in the regulatory process. EPA o±cials identi¯ed nearly 40 published original articles and requested that the investigators reanalyze their data using alternative methods to GAM. The re-analyses were peer reviewed by a special panel of epidemiologists and statisticians appointed by the Health E®ects Institute (HEI). Results.
