As noted in the LA Times obituary:
"If you can put a number on it," Arthur C. Nielsen Jr. said his father once told him, "then you know something."
It was a lesson the younger Nielsen — who died Monday at age 92 — never forgot. His lifelong efforts remade his father's once-obscure Chicago market research firm into a sprawling, worldwide measurement giant with a brand name that, in the U.S. at least, became a household synonym for television ratings.
Today — even after his company has undergone ownership changes, not to mention weathered near-continuous industry complaints of supposedly flawed methodology — TV executives still arise before dawn to check out the Nielsens, foretelling the fate of their shows and their careers with each ratings point. In recent years, the company has expanded into measuring online traffic and other new media.