One of the UK's leading UFO researchers, Jenny Randles, has kindly given me permission to upload a searchable scanned copy of her book "UFO Reality" (1983). I have added to the books folder in my online archive, hosted by the AFU.
Anyone looking for a balanced introduction to ufology and an overview of relevant issues (or who wants to develop critical thinking about UFO evidence) will struggle to find many better books for those purposes, even 40 years later.
This was the first book in which Jenny Randles used the term "Oz Factor". Jenny wrote about UFO witnesses reporting a "sensation of being isolated, or transposed from the real world into a different environmental framework". She commented that this sensation "is almost suggestive of the witness being transported temporarily from our world into another, where reality is similar but slightly different. A world where miracles can happen". She noted that this effect "common and important" and adopted the name "the Oz Factor" for it, after the fairytale land of Oz. Jenny suggested that it is "as if a spell is cast by the famous magician from that land, taking the witness into a new reality".
This book was also part of the development of another term: "UAP". Starting with her books in the early 1980s, including this one, Jenny Randles started the popularisation of the term "UAP" as a potential replacement for the term "UFO". Her book "UFO Study" (1981) was her first book to use the term "UAP". She also used the term "UAP" in "UFO Reality" in 1983, giving reasons for preferring the term "UAP" (which she then used to stand for "Unidentified Atmospheric Phenomenon"). Her books gradually influenced other researchers. The term "UAP" has been used infrequently before Jenny's work, but became considerably more popular as Jenny's influence spread amongst ufologists.
(I therefore find it amusing that one UFO researcher has repeatedly falsely claimed in lectures and podcasts that he coined the term "UAP" in around the year 2000. This, of course, is decades after the term was initially used and several years after quite a few UFO researchers used the term. Luckily for that researcher, most of his audience appears unaware of the falsity of his claim...).