In a 1990 paper published in the "Journal of Scientific Exploration", computer scientist and ufologist Jacques Vallee, presented a compelling argument against the extraterrestrial origin of UFOs.
In it he broke the various phenomena down into five distinct categories of discussion.
Close Encounter Frequency
Physiology
Abduction Reports
History
Physical Considerations
From the papers conclusion:
Exciting as an extraterrestrial visitation to earth would be, this paper has pointed out that in the current state of our knowledge UFO phenomena are not consistent with the common interpretation of this hypothesis.
Neither do the observed patterns support the theory that all UFOs can be explained as combinations of natural effects, or as psycho-sociological processes.
by esosecretgnosis