[zaarn]

Or possibly noone did a study of sufficient size that passed peer review.

It's also not hard to make the pay gap 1-2% just like it's not hard to make it 25% (both values are valid). Statistics is a fun field. Don't trust statistics you didn't fake yourself.

Amazon could easily cook the numbers to get to 1-2%, I doubt anyone checked the process of determining that number if it's unbiased and fair and accounts for other factors or not.