This article accompanies The Feminization of HR.

PayScale Inc. has explored the possible differences in pay between men and women in HR positions in a variety of ways.

Both uncontrolled pay -- pay that is calculated without adjusting for outside compensable factors, such as job title, years of experience, company size, etc. -- and controlled pay are examined.

The controlled pay takes into account compensable factors other than gender, and calculates pay on a level playing field, answering the question, "If everything except gender was exactly the same, what would the pay be?"

Seattle-based PayScale also explores differences in education, age, stress and satisfaction.

See the charts here.