This idea of "published" can (and is) relaxed though. Indeed it is my perception that in many topic areas we rely far too heavily on online sources - there can be a distinct prejudice against offline source material.
Tom
Journals pose a particular problem as they are often, as in the case of the three journal articles in this case, behind pay walls. Those are peer reviewed, while his book by a commercial publisher has not received academic reviews.
Someone did send me a copy of one of the academic journal articles. But I have yet to see the other two which cost quite a bit.
Fred