title: Oral clefts with associated anomalies: methodological issues.
abstract: OBJECTIVE
  To discuss methodological factors that account for the wide variation in the reported prevalence rates of anomalies associated with oral clefts.
  
  
  CONCLUSIONS
  The published prevalences of associated anomalies vary considerably because of the following: (1) differences in case definition and inclusion/exclusion criteria; (2) length of time after birth that cases are examined; (3) variability of clinical expression of associated anomalies; (4) knowledge and technology available to produce syndrome delineation; (5) selection of patients, sources of ascertainment, and sample size; and (6) true population differences and changes in frequency over time.
authors.affiliation: Boston University School of Medicine, Massachusetts 02118, USA.
authors.forename: Diego F
authors.initials: DF
authors.lastname: Wyszynski
authors.forename: Andrea
authors.initials: A
authors.lastname: Sárközi
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Czeizel
mesh_terms: D015982:Bias; D002971:Cleft Lip / Q000453:epidemiology*; D002972:Cleft Palate / Q000453:epidemiology*; D000013:Congenital Abnormalities / Q000453:epidemiology*; D004812:Epidemiologic Methods; D006801:Humans; D013677:Medical Laboratory Science; D018579:Patient Selection; D019683:Penetrance; D015995:Prevalence; D018401:Sample Size; D013577:Syndrome; D013997:Time Factors