title: Probability and likelihood in genetic counselling.
abstract: The aim of this paper is to clarify some of the concepts used in the calculation of risk in genetic counselling. The use of probability as a measure of risk in a particular case is reviewed, with special reference to the Fisher-Neyman controversy. The technical concept of likelihood is then introduced and applied to risk probabilities themselves. The difficulties of interpretation are discussed, with a distinction drawn between calculating the risk for a child and inferring the genotype of his mother, even though the risk is wholly determined by the genotype. Fiducial inference is briefly mentioned, and the paper ends with a discussion of the problem which arises when the functional relationship between an unknown parameter and the unknown risk is not 1:1. The conclusion is tentatively reached that risk can only be gauged by probability and thus that prior probabilities must sometimes be assumed, but the paper is primarily intended as a guide and catalyst for the informed discussion of some of the difficulties, which may involve ethical dilemmas.
authors: Department of Community Medicine, University of Cambridge, England.
authors: A W
authors: AW
authors: Edwards
mesh_terms: D005817:Genetic Counseling / Q000706:statistics & numerical data*; D006801:Humans; D016013:Likelihood Functions; D011336:Probability