bayesian analysis Flashcards
3 ways to calculate a risk or recurrent risk figure
- Diagnosis and mode of inheritance
- Analysis of family pedigree
- Results of tests – linkage studies etc.
prior probability
initial probability
- based on anterior (ancestral) information
Conditional probabilities
determined using modifying observations
- based on posterior information
e. g. numbers of offspring / results of tests etc.
Joint probability
prior probability (1) x conditional probability (2)
Posterior / relative probability
joint probability divided by the sum of all joint probabilities
additional factors - Autosomal dominant inheritance
- Reduced penetrance - Delayed age of onset - # affected offspring
additional factors -
Autosomal recessive inheritance
- Carrier risks for extended family
- Modifying carrier risk by mutation analysis - # affected offspring
additional factors -
Sex-linked recessive inheritance
- Incorporating carrier test results - # affected offspring
if penetrance is 80%. what is the chance of an affected child from an unaffected parent.
what is the posterior information and why
0.2
as there is a 20% chance of being a carrier and unaffected. which is required for an affected child
prior probabilities for autosomal recessive diseases
if the parent is unaffected, there is a 2/3 chance of being a carrier as there is no chance of being homo recessive. thus not 2/4
assuming there is a posterior probability of 1/750 for an autosomal recessive disease with no family history and the father is a carrier. what is the chance of an affected child
risk of carrier (father) = 1
risk of carrier (mother) = 1/750
risk of child receiving 2 mutant alleles = 1/4
1/4 x 1/750 x 1 = 1/3000
how to calculate joint probability from multiple conditions
multiple all conditions by prior
