Sighting reports of UFO entities date back to the late nineteenth and early twentieth century. The quantity of such reports has been steadily increasing, peaking in the late sixties and seventies. About 15% of known entity cases are those where the witness(es) are alleged to have been taken on board a craft--the so called "abduction" cases.
The reader should be aware that the fraction of true abduction cases is likely underestimated for various reasons. These include the abductee's fear of ridicule, an externally applied or subconscious repression of the event, and inaccessibility of the cases from the files of investigators.
These reports are important to an understanding of the UFO phenomenon because: the chances for misidentification by the witness are minimal; the amount of information per report is usually large; and, because some close encounter cases involve witness(es) having been reportedly taken aboard the UFO, they could be the key to our understanding of the UFO problem.
The investigator cannot afford to arbitrarily dismiss any entity report no matter how high a degree of "strangeness" it may seem to have. The keys to acceptability are witness credibility and careful documentation.
The following is written assuming that the reader has had experience with UFO reports, but not specifically with entity reports.