In BBT forums I have read several posts regarding ruling in and out policies, such as 1 homozygous or 1 homozygous and 2 heterzygous. Has anyone based their rules on published studies? Does anyone know of any published studies in which ruliing out methods were compared?

See the AABB Technical Manual, 16th Edition, p. 473.

Also, if you go into the BCSH Guidelines website, and look under the Pre-transfusion Testing Guideline (can't think of the exact title at present) it's in there "Chapter and Verse" (although, of course, you have to recognise these are UK Guidelines, and so do not apply to the US of A).