Why don't people take Donald Trump seriously? He's ahead in the polls, he built a tremendous empire, made more than $200 million for his work on The Apprentice, wrote the best-selling business book of all time, went to the Wharton School of Finance--

Wait, what? Go back to that thing about the biggest-selling business book. Here's Trump on CNN a few weeks back:

They like to say, well, we don't consider him a serious candidate. Why wouldn't I be? I went to the Wharton School of Finance, I was a great student. ... I go out, I make a tremendous fortune. I write a book called The Art of the Deal, the No. 1 selling business book of all time, at least I think, but I'm pretty sure it is. And certainly a big monster, the No. 1 bestseller. ...

I remember reading The Art of the Deal in high school, or at least buying it and giving it as a gift to someone. (It was probably my dad. I buy him a lot of books for presents.) It was definitely popular at the time, but potentially the most successful business book ever? A website called Politifact, run by the Tampa Bay Times newspaper, decided to examine Trump's claim by digging up sales data on what appeared to be the seven most successful in the genre--defined very broadly.

What we know: Trump's book was on the New York Times bestseller list for 51 weeks, and reportedly sold more than a million copies. Those claims are really hard to verify, but according to Nielsen Bookscan, Trump has sold about 177,000 copies since 2001.

Here's what Politifact came up with.

1. How to Win Friends & Influence People

A 79-year-old classic, Dale Carnegie's How to Win Friends & Influence People has sold 15 million copies according to its publisher. Since 2001: 2.27 million copies.

2. The 7 Habits of Highly Effective People

First published in 1989 (two years after Trump's book), its publisher claims Stephen Covey's The 7 Habits of Highly Effective People has sold between 10 and 25 million copies sold. (Quick time out, that's a heck of a range, but anyway, according to Nielsen: 2.18 million copes since 2001.

3. Rich Dad Poor Dad

This one surprised me, but since its publication in 2000, Rich Dad Poor Dad has legitimately sold 6.99 million copies according to Nielsen. As of 2004, according to the New York Times, there were 24 million copies of author Robert T. Kiyosaki's books in print, including several titles in the series.

4. Steve Jobs

Finally, we get to a title that was published post-2001, which means we can gauge its total sales with some clarity: 3 million according to the publisher, 1.74 million according to Nielsen Bookscan. Not bad, Walter Isaacson!

5. The Art of the Deal

Here's Trump's book on the list, with his publisher claiming 1 million copies sold, and 187,000 showing up on Nielsen Bookscan--but only since 2001. For the record, that's way more than my books ever came close to selling.

6. Competitive Strategy

In its 60th printing in English, and with 19 foreign language edition, this is Harvard Business School Professor Michael Porter's 1998 classic theory of business strategy. It's sold 70,000 copies since 2001, but the publisher doesn't seem to estimate total sales.

7. In Search of Excellence

Last on Politifact's list is McKinsey consultants Tom Peters and Robert Waterman's 1982 book was described by Bloomberg as "the top-selling management book of all time," although with its publisher claiming only 3 million copies sold, that's hard to square. Since 2001: 54,000 copies.

It's easy to find fault with Politifact's list. It's missing some obvious titles, such as Jim Collins's Built to Last andKen Blanchard and Spencer Johnson's The One Minute Manager--to say nothing of titles like The Prince by Machiavelli and The Art of War by Sun Tzu. Regardless, it seems clear that while The Art of the Deal might belong in a discussion of the best selling books in its genre, there's no way it's actually the most successful.