On average, U.S. women make $.74 on the dollar compared to men.
Some studies say more, and some less. But the fact that women earn less than men in general is not a myth; it's an inarguable fact.
That said, it's a fact that's used out of context or misunderstood. A lot.
While it's true that, typically, women make less than men for doing the same jobs, that discrepancy is not nearly as large as the $.74 to the dollar figure. This oft-cited figure comes from the fact that men and women tend to hold different jobs.