I don't know if this could be measured, but my belief is that, broadly speaking, employers don't pay for experience quantitatively in terms of years in the industry but rather tend to pay for more qualitative metrics like past positions held, roles, and skill-sets. It's easy to say "I've been a DBA for 12 years.", but the problem is that most respondents could not accurately evaluate themselves on the more qualitative metrics. Even a question like what specific technologies the respondent has experience with is subjective. I guess the best way to frame the question would be "Do you use XYZ in your professional career, and do the people you report to at work regard you as experienced with XYZ? Yes / No", rather than simply "Do you know XYZ? Yes / No". It's more about people's impression of your knowledge and experience that determines your salary, not your own personal opinion. It is still possible for talented and experienced people to be under-rated or under-utilized, thus resulting in a lower salary, however, your own personal opinion is still important for other reasons, like giving your the confidence to move on or move up to another position that better leverages your talent.