association study confusion

[alt42]

hi all,

 

i'm trying to include some population genetics information in a paper i'm currently writing and i've come across a problem with a paper i'd like to use. the pubmed link is as follows (i also attached the paper):

 

http://www.ncbi.nlm.nih.gov/pubmed/16804517?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum

 

Now for my two questions:

 

1.) what is the difference between relative risk (RR) and genotype relative risk (GRR)?

 

2.) what do the numbers under the different models in table 2 mean? why does recessive model have infinity for each study included in the meta-analysis?

 

i'm thinking the values i asked about above describe the likelihood of each model but how do i know which ones are significant and which ones are not

Association of MUTYH and colorectal cancer.pdf

[MedGen]

I've just had a cursory glance at the paper, but the GRR merely reflects how they have treated each genotype as an independent event for the purposes of calculating risk.

 

As for your second question, the numbers are the relative risk (RR) followed by the 95% confidence intervals. Relative risks (and odds ratios) are not informative unless the 95 CI's are also stated which reflect the level of variation in RR's within the cohort. Where 95% CI starts below 1.0 you can see that there are some individuals who might carry the risk genotype under that model and not have the disease (in this case colorectal cancer). This likewise applies to RR below 1.0 (i.e. associated with a protective effect) where the 95%CI rises considerably above 1.0 then you will have healthy controls carrying the risk genotype but not suffering from the disease. It is generally a good indicator (though not an accurate one) of some of the within-cohort heterogeniety (this should actually be tested for between the studies to confirm associations are genuine and not down to chance, which they have done with both a fixed and random effects model).

 

As for the infinity symbol this might be a reflection of the low numbers of MM genotypes, and thus they are dividing by zero when calculating the RR for that model in a lot of the studies.

 

Hope that answers your question.