This is never going to be accurate. Titles alone are a poor indicator of ability in software.

E.g. I hold the title of "Senior Software Engineer" despite only have 2 years/4 mo. of experience and very little of that experience is project management or non-code things.

When talking to recruiters in my area for a new position and giving a base salary of $90k, they routinely come back with "You won't get that offer with your level of experience".

In practice, I routinely cut the Senior from my title to avoid expectations I can't meet.

Dice.com has a much better idea behind this, which is tying skills and years of skill to estimated salary. The backend for LinkedIn's site honestly does not look more complex than a few straight-forward SQL queries.