Cities close together in the standings may have very different prices, while others further apart can be effectively level with each other, taking into account margins of error for price and expenditure data, which the firms don't share with the public.

WSJ: Useful Cost-of-Living Data Don't Come Cheap

Later that month a representative indicated that the capital gains distribution credited to her account was a computer error.

FORBES: Sodexo's Twisted 401(k)

Having established the reality of his point, he then designed a mathematical model that tried to take into account and quantify sources of error.

ECONOMIST: Just how reliable are scientific papers?