davidjohnson6, I don't know the background to the research but no, these numbers won't have been validated by an independent organisation as it wouldn't be feasible to do so. It would only be possible to validate their estimation techniques which I assume, although don't know, forms part of the observer role which included the European Commission.
I don't see why you call it a strong conflict of interest, yes clearly it's in the European Regions Airline Association interest to highlight the maximum number of jobs that they believe is created by aviation, however they will only achieve any recognition of their claims through the use of acceptable and adequate research techniques. Given the organisations willingly putting their names to this and the fact that the European Commission acted as observers, again I can only assume that there is solid basis for their claims.