Benford's law

Benford's law, also referred as first digit law, is a principle that in any large random real-life sets of numerical data, around 30% numbers begin with 1, around 18 percent begin wit 2, and so on, very small data begins with leading digit 9.  It is a frequency distribution law of nature.

Simon Newcomb, american astronomer, noticed in 1881 that first few pages of logarithm books are used more.  Frank Benford, physicist, paid attention to it in 1938. He collected data from 20 different domains like surface areas of rivers, sizes of populations, physical constants and numbers from a reader's digest magazine.

References
Wikipedia Benford's law
Wolfram Mathworld page