Alternatively - men and women experience similar levels of stress from major life events, but women are more comfortable reporting it. You notice the event with the smallest difference, the birth of your first child, is the one event men have constantly been told it's OK to worry about for decades.
There is absolutely zero excuse for such sloppy and crappy studies. Stress has it's own hormones, it's own metabolic byproducts, and it's own physiological effects. A study relying on self reporting is about as useful as phrenology.