Lecture 8: Association analysis Flashcards
What is the purpose of an association analysis?
To establish a disease trait and a genetic marker.
Design types of association analysis:
1) Case-control - select indivuals stratified on sex, age and other covariates
2) choose indiviuals from existing cohort - to the extent that it is possible choose covariates that are the same in the two groups-
How is selection basis often introduced?
Convenience sampling - instead of proper stratification we just do what is cheap and easy.
How does association analysis test if a marker has a dominant inheritance pattern?
You aggregate the Aa and AA in the cases/control genotypes table and do a chi-square test.
How does association analysis test if a marker has a recessive inheritance pattern?
Same as dominant but aggregate.
How is the co-dominant model tested in association analysis?
Don¨t aggregate.
What is the alleles test?
The test investigates if the allele frequencies are the same in the case and control group. It assumes HWE:
p_control = p_case
What does the trend test investigate?
Instead of p it uses the conditional mean of the amount of alleles:
E[X | case] = E[X | control]
What is the purpose of an exact test?
When the sample size is small the assumption that data follows a given distribution is unlikely.
An exact test finds all possible outcomes, and the exact probability can be calculated from this.
What is the risk ratio?
P(disease | exposed) / P(disease | unexposed)
What is the odds ratio?
P(disease | exposed) / P(healthy | exposed)
/
P(disease | unexposed) / P(healthy | unexposed)
What is the power of a model?
The probability of getting a significant result at a given effect size.
