As a former compensation officer for the government, I would only guess the reason for the pay difference between the genders would be different levels of duties and responsibilities. Each position description is matched with position classification standards from the Office of Personnel Managment and a determination is made on the correct salary level.

I could go on about position classification in the Federal government but it would lead to eyes glazing over and people falling asleep on their keyboards. My wife and daughter would always roll their eyes when I came home from work and said, "Let me tell you a funny classification story that happened at work today."