My name is Ralph Betza; I'm a chess master ( FM ), and a computer programmer. I'm not a mathematician or a statistician (nor do I play one on TV), though perhaps I should be in order to investigate this subject.
I also have some fame as an inventor of "Chess Variant" games; some of my games are played in postal World Championships. I became interested in the subject of piece values as a result of one of the games I invented, in which White and Black have different armies.
These are my qualifications for the task of researching and writing about the values of chess pieces.
The work you are reading is the result of 20 years of my study of this subject! Not 20 years full-time, of course; just now and then, and every year or so I add a new idea.