I’ve heard that having a published book is more highly respected than having a Ph.D. I’m not sure if this came from research, the author’s opinion, or merely emerged as a clever quip. But, it does give me pause.
In completing a PhD there is (usually) a dissertation to produce. A dissertation is the length of a book and is much more tedious to write. And upon its completion, the dissertation is published (albeit in the technical sense). I’ve done this twice.
Writing a book is much easier than a dissertation or thesis; it requires less time and effort. I’ve done this, too. And it’s not hard to publish a book either, assuming you self-publish. (In the past, many notable authors self-published.)
However, it is much harder to go the traditional route and find a publisher who will produce mass quantities of your book in printed form and distribute them around the world. I have yet to do this.
What’s interesting is that in non-fiction, publishers look for writers with the authority to cover their topic; they seek credentials. A Ph.D. in your field is a prime credential.
So even though I consider earning a Ph.D. harder—and therefore more worthy of respect—publishing a non-fiction book often requires a Ph.D. anyway.