[z3c0]

While I believe "boldness" is more related to personality than to gender, I have noticed the "bragging bias" you've described quite a bit. But it goes both ways. That is to say "people respond to surveys when they have something to say." If you believe you're being paid too little, you're just as likely to chime in as somebody who wants to brag about their pay. It's the folks in the middle who end up not chiming in, out of the belief that they have little insight to offer. Because of this, ootional surveys oftentime yield biases towards the extremes.

Source: I've analyzed survey data a lot

[chiefalchemist]

Multiple studies show men on average apply for jobs they are not fully qualified for. Women on the other hand are more "conservative" and take less risk (so to speak).

Yes, of course, there are variations from person to person, sans gender. But there are also gender-centric cultural norms.