title: Optimal referent selection strategies in case-crossover studies: a settled issue.
authors.affiliation: Cardiovascular Epidemiology Research Unit, Beth Israel Deaconess Medical Center, and the Department of Medicine, Harvard School of Medicine, Boston, MA 02215, USA. mmmittlem@bidmc.harvard.edu
authors.forename: Murray A
authors.initials: MA
authors.lastname: Mittleman
mesh_terms: D000397:Air Pollution / Q000009:adverse effects*; D016022:Case-Control Studies; D018592:Cross-Over Studies; D006801:Humans; D012107:Research Design; D015983:Selection Bias