Citing a self-help book

I've noticed several articles cite that procrastination rates may be "as high as ninety-five percent." My impression was that this number was frequently cited because it was the highest, not because it was the most accurate. I flipped to the reference page. The reference? Overcoming Procrastination, published by the Institute for Rational Living. I was a bit concerned that we were citing a book here, not a study. And not the most scholarly sounding book at that.

I requested the book. I opened it to the first page. Here's the opening:

How many college-level individuals procrastinate? Often? Seriously? No one seems to know. Incredibly, this important question has not inspired many factual studies. Our guess? About ninety-five percent. (Ellis and Knaus 1)

So it's just a guess? And this thirty-year-old guess is still being cited? The authors aren't even researchers; they're psychotherapists. Which is not to say they don't know what they're talking about, but rather to ask why on earth serious researchers keep citing them instead of doing some actual research on the numbers. I wonder if some of the citations were borrowed from other sources without checking the original source. It's not a scholarly source. It's a self-help book.

Work Cited

Ellis, Albert, and William J. Knaus. Overcoming Procrastination, or How to Think and Act Rationally in Spite of Life's Inevitable Hassles. New York: Institute for Rational Living, 1977.