title: Estimation and the nature of controls in birth defect studies.
authors.forename: E B
authors.initials: EB
authors.lastname: Hook
mesh_terms: D015982:Bias; D016022:Case-Control Studies; D000013:Congenital Abnormalities / Q000453:epidemiology*; D004314:Down Syndrome / Q000453:epidemiology; D006801:Humans; D016017:Odds Ratio; D012907:Smoking / Q000453:epidemiology*