title: Measures of familial aggregation depend on definition of family history: meta-analysis for colorectal cancer.
abstract: OBJECTIVE
  Familial aggregation, a primary theme in genetic epidemiology, can be estimated from family studies based on an index person. The excess risk due to the presence of affected family members can be classified according to whether disease in the relatives is considered a risk factor for the index person (type I relative risk) or whether the disease status of the index person is considered a risk factor for the relatives (type II relative risk).
  
  
  METHODS
  A meta-analysis of published colorectal cancer studies reporting a measure of familial association was performed and application of multilevel linear regression to model age-specific relative risks presented.
  
  
  RESULTS
  The pooled type I relative risk of colorectal cancer given any affected first-degree relative (based on 20 studies) was 2.26 (95% confidence interval CI = 1.86, 2.73) and decreased with the age of the consultand. The pooled type II estimate (based on seven studies) was 2.81 (95% CI = 2.05, 3.85).
  
  
  CONCLUSIONS
  Type I relative risks are useful in clinical counseling settings when a consultand wants to know his/her disease risk given his or her family history. Type II relative risks can be used to quantify the risk of disease to relatives of an affected individual and then identify subjects eligible for screening.
authors.affiliation: Cancer Epidemiology Centre, The Cancer Council of Victoria, 100 Rathdowne Street, Carlton, Melbourne, Victoria 3053, Australia. laura.baglietto@cancervic.org.au
authors.forename: Laura
authors.initials: L
authors.lastname: Baglietto
authors.forename: Mark A
authors.initials: MA
authors.lastname: Jenkins
authors.forename: Gianluca
authors.initials: G
authors.lastname: Severi
authors.forename: Graham G
authors.initials: GG
authors.lastname: Giles
authors.forename: D Timothy
authors.initials: DT
authors.lastname: Bishop
authors.forename: Peter
authors.initials: P
authors.lastname: Boyle
authors.forename: John L
authors.initials: JL
authors.lastname: Hopper
mesh_terms: D017668:Age of Onset; D015179:Colorectal Neoplasms / Q000235:genetics*; D030342:Genetic Diseases, Inborn / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D006801:Humans; D016014:Linear Models; D010375:Pedigree; D012306:Risk