When you read the source text, you can see that they have been fairly selective in the criteria in which they dismiss size of the wage gap. I would argue that the text shows the study was produced with a political leaning. http://www.ncpa.org/pub/ba766

"O'Neill finds that single women without children, on average, make 8 percent more than their similarly situated male colleagues"

http://www.ncpa.org/sub/dpd/?Article_ID=22058#sthash.6sSZrCm...

You can see how that is a narrow selection though? Men and women don't remain 'similarly situated' throughout their entire careers, particularly when you factor in child-rearing (paternity still being highly uncommon, and few countries offer it as a social benefit).

In in simplest form that is like saying "the pay divide between women and men is non-existent when women are effectively men."

The data sourced here are full-time only workers, not part-time.

Would love to take a look at the souce code of that analysis, but I can't find it. Happen to know where I can get it?