Whipple's Index

Whipple's Index (index of concentration) is an indicator of the degree of age heaping. It is obtained by summing the age returns between 23 and 62 years inclusive and finding what percentage is born by the sum of the returns of years ending with 5 and 0 to one-fifth of the total sum. The UN recommends a standard for measuring the age heaping as follows:

Applicability
Respondents to a census or other surveys sometimes inaccurately report their or other household members' age or date of birth. Whipple's Index is applied to detect the extent to which age data show systematic heaping on certain ages as a result of digit preference or rounding. Although Whipple's Index has been widely applied to test for age heaping, it assumes that the heaping is most likely to occur in 5 and 10 year intervals or some other fixed interval based on digit preference or rounding.

In some cultures, however, heaping may display a different pattern. For example, it has been shown that among Han Chinese, age heaping occurs on a 12-year cycle, consistent with preferred animal years of the Chinese calendar. Whether this heaping represents actual fertility behavior (e.g., bearing children in favorable animal years) or selective memory or reporting of year of birth has not been determined. Although the heaping is not severe among Han, and it does not seem to be associated with age exaggeration, it is systematic and is higher among illiterate populations. On the other hand, among Turkic Muslim populations in China (Uyghurs and Kazakhs in Xinjiang Province) there is severe heaping at ages ending in 0 and 5; it is much higher among illiterate populations and appears to be correlated with age exaggeration. These traditionally Muslim nationalities do not use the Chinese calendar.

This finding suggests that use of Whipple's Index or other measures of age heaping that focus on specific digits or on decimal intervals of the age spikes may not be appropriate for all populations. In the case of China's 1990 census reported above, among Han heaping was found at ages 38, 50, 62, 74, and so on — ages that corresponded with being born in the Year of the Dragon. But among Turkic Muslims, heaping was found at ages 35, 40, 45, 50, 55, 60, and so on and increased in magnitude with age.

External link

 * Age Validation of Han Chinese Centenarians (an example of the Whipple's Index applied)