Your guess
How often does a number in real-world data start with a 1?
Well-thumbed pages
In 1881 the astronomer Simon Newcomb noticed that in books of logarithm tables, the pages for numbers starting with 1 were far grubbier than the rest. In 1938 the physicist Frank Benford tested the idea on data from 20 fields – from river areas to death rates.
Why the 1 stays in front so long
A fund worth $100 million grows by 10 % a year. Getting to $200 million – the whole time a 1 is in front – takes just over 7 years. From $900 million to a billion takes only about a year. Then it starts again at 1. The same holds for anything that grows steadily or even erratically.
Made-up numbers stand out
In 1993 a manager at the Arizona state treasury was convicted of steering nearly $2 million to a sham vendor through 23 cheques. Over 90 % of the amounts began with 7, 8 or 9 – almost the opposite of Benford. Auditors and tax investigators now look for patterns like this.
