In all honesty, I pulled those numbers out of a hat
Today my blog received a lot of traffic about this post from yesterday about the relative risk of disease genes. I wrote that the relative risk (RR) of the genetic variants we have discovered recently using genome wide association studies are rather small -- 1.1 to 1.5 -- and that such a small increase did not matter that much, all in all, and that I doubted that it would have much of an impact for us to know we have a gene that increases our risk that little.
All of this I stand by. The numbers for the relative risk are also consistent with the papers I've read, but I have not done a proper survey to see the actual distribution of the RRs. I am thinking about doing that now, but it is not quite as simple as it sounds to figure it out. There is something called "the winners curse" that essentially means that our estimates of the relative risk tends to be higher than the risk really is, because we estimate the risk from a biased sample: the sample where we discovered the risk in the first place. See Zöllner and Pritchard: Overcoming the winners curse for more on this.
I gave an example, however, where I said that increasing the risk of cancer from 0.1% to 0.15% -- a relative risk of 1.5 -- would have no consequence what so ever. Those numbers I just made up. I intentionally picked very small numbers to make a point, but it is a bit dishonest. I don't know what realistic numbers would be, to be absolutely honest, but these are probably way too small for any "interesting" disease.
If the risk of a disease, without "risk genes", is 0.1% I don't think we would bother with it in the first place. It would be pretty hard to find enough cases for a study anyway.
Realistic numbers might be 5% to 7.5% or 10% to 15%. I don't think it changes my point: people are not going to change their habits for such an increase in risk when the do not change their habit for much larger risks such as diet, exercise, smoking, drinking, etc. As Genome Technology Online puts it: That's Because Risk Is Small and Inertia Is Great.
Anyway, I shouldn't have made up numbers like that -- even as an informal example to make a point -- and I wouldn't have if I knew this many people would read it...
Now I should probably go figure out some accurate numbers so I don't make the same mistake again.