Project Blue Book Special Report 14
Dr. Leon Davidson and CSI-NY were instrumental in getting this document release in the middle of an era when the Air Force denied most requests for UFO information or actual reports. Then, it was only with the Moss Govt Info Subcommittee's intervention that the Air Force made a copy available. Davidson had to promise not to turn a profit on any reproduction. Davidson's commentary on the report was telling. Battelle obscured the Chi-Square test that showed there was a statistical difference between knowns and unknowns. How the Insufficient Info cases are known is still beyond me. They are, in fact, rejected cases and should not be included in a serious study. The problem of the Air Force definition of a UFO case was never handled by Battelle.
As Ruppelt said, this report was junk.
It had a selection effect in that military and govt installations which have 24/7 attention to area surroundings were over represented.. Obviously a govt entity with the force of law is going to get govt reports rather than voluntary reports from the public. Also as Loren Gross stated he looked at every frame of Project BB for 1947-1959. Compared to APRO (microfilm of cases pre-Arnold to Dec 1956 available) and NICAP and CUFOS files, there is very little overlap of reports except the few which receive large press coverage. (I want to say that reading all of Gross' booklets he probably did not consult the OSI UFO files microfilms, however he did have access to about a quarter of the 4602d AISS cases mid 1954-1956 from the NARA which I copied during my research there.)
Finally we do not know the exact sample used by Battelle. The report indicated that USAF reports were used, but it also said that letters and other sources were considered.
Pre-Arnold cases were not considered even where it could be established that the incident was reported prior to Arnold.