Whipple's Index

Whipple's index (or index of concentration) is a method to measure the tendency for individuals to inaccurately report their actual age or date of birth. Respondents to a census or other surveys sometimes report their age or date of birth to make it seem more culturally favorable, for example to apppear younger, or to be born on a date that is considered luckier than their actual date of birth.

The index was invented by American demographer George Chandler Whipple (1866–1924) is applied to detect the extent to which age data show systematic heaping on certain ages as a result of digit preference or rounding. Typically the concern is for heaping on particular ages such as those ending in 0 and 5.

The index score is obtained by summing the number of persons in the age range 23 and 62 inclusive, who report ages ending in 0 and 5, dividing that sum by the total population between ages 23 and 62 years inclusive, and multiplying the result by 5. Restated as a percentage, index scores range between 100 (no preference for ages ending in 0 and 5) and 500 (all people reporting ages ending in 0 and 5).

The UN recommends a standard for measuring the age heaping using Whipple's Index as follows: