The UFO problem is perhaps closer to astronomy than physics. No single observation of the position of a single planet establishes Kepler’s law. No single observation of the position and magnitude of a single star establishes that the sun is in a disc-shaped galaxy. Nor can data concerning a single star confirm a proposed theory of stellar evolution. In discussing astronomical problems, it is essential to combine evidence derived from many observations. The strength of the observational facts may become significant only when very large numbers of observations are combined.

Following astronomical practice as a guide, one would infer that a crucial first step in the scientific study of UFOs would be the compilation of a catalog. This would have the immediate consequence of drawing upon information already accumulated (in many cases with great effort and great care) by other organizations. For instance, organizations such as APRO (Aerial Phenomena Research Organization), CUFOS (Center for UFO Studies), MUFON (Mutual UFO Network), and NICAP (National Investigation Committee for Aerial Phenomena) have compiled extensive files of UFO cases using careful screening and evaluation techniques. One valuable collection of data, which the project could have used, was that produced by the Battelle Memorial Institute, under contract to the Air Force, and issued as Blue Book Special Report No. 14. This was certainly available to the project, since it was declassified in 1955.

There is, indeed, great advantage to be derived from using more than one source of data. Data derived from one source only might be spurious, or partly spurious, and the same might be true for another source of data. If both sources of data yield distinct and irreconcilable patterns, one would suspect that at least one of the two sources has been subject to biased reduction and possibly even to deliberate fabrication. If one of the sources of data is from one’s own scientific staff, one might conclude that the fault lies with the other group, or one might choose to check carefully the methods used by one’s own team.

On the other hand, patterns that appear consistently in data derived from several sources are far more significant than a pattern that shows up in the data of one source but not in the data of other sources. “Strong” facts of this type can be obtained only by careful cataloging of data from as many responsible sources as one can find. After a catalog has been compiled and patterns supported by the weight of evidence in the catalog have been established, one can then begin the comparison of evidence and hypotheses. (An outstanding example of this process is the construction of the Hertzsprung-Russell diagram in astrophysics, which provides the crucial test for any theory of stellar evolution.) This procedure is complex, calling for a careful organization of theoretical work and data reduction. A “bookkeeping” procedure for organizing the many judgments involved in this stage of scientific research has been proposed elsewhere (Sturrock, 1973), with application to astrophysical problems in mind. Some subsequent comments on the scientific study of UFOs are based in part upon this article.