I think I need some clarification about what it means to be a "case" but have 0 at risk alleles? the table specifies that this is 500.
I don't think I understand what we are being asked to do because of this X=0, 500 cases category, as this does not contribute to disease in terms of my understanding of dominant, recessive and co dominant inheritance.....
thank you
Laura
In this question, when we state "Compute chi square tests for codominant, dominant and recessive modes of inheritance" what is really meant is "Compute chi square tests for codominant, dominant and recessive coding of genotypes". It's not that we know the particular mode of inheritance, but rather how we code the genotypes for analysis. For example, a dominant coding would collapse X=1 and X=2 together into a single exposure group and compare them to X=0.
Can you or someone review slides 14-17 again?
your explanation to the above seems logical but when trying to relate it to the lecture material, I can't figure out how they compare. for example, is the C allele the risk allele in the slide material, and would it be equivalent to the X=1 or 2 alleles? So that the TT genotype is equivalent to the X=0 in question 3? So in your example of dominant above, you are adding X=1 and X=2 which is equivalent to adding CC and CT?
2 df Genotype Recessive (G) Dominant (G)
Genotype Case Control Case Control Case Control
CC A D CC A D CC or CT A+B D+E
CT B E CT or TT B+C E+F TT C F
TT C F
~chi_sq(2df) ~chi_sq(1df) ~chi_sq(1df)
Yes this is correct.
one last question. For co-dominant, according to the references I looked at, you need two different risk alleles. this question doesn't specify whether X=2 reflects two different alleles. It is clear as mud to me how to create a situation for co-dominance from the information given in the question. Would appreciate further discussion about this, or additional reference to read about the calculations presented in slides 14-17
thanks
Co-dominant is the 2 df test used in slide 16. You compare the two genotypes (X=1, X=2) versus the null (X=0). Two different ORs are calculated.
