Whipple's Index
Encyclopedia
Survey
or census
respondents sometimes inaccurately report ages or dates of birth. Whipple's index (index of concentration), invented by the American demographer George Chandler Whipple (1866–1924), indicates 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 Whipple index score is the five times the percentage of persons in the age range 23–62 inclusive, who report ages ending in 0 and 5. 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:
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.
Statistical survey
Survey methodology is the field that studies surveys, that is, the sample of individuals from a population with a view towards making statistical inferences about the population using the sample. Polls about public opinion, such as political beliefs, are reported in the news media in democracies....
or census
Census
A census is the procedure of systematically acquiring and recording information about the members of a given population. It is a regularly occurring and official count of a particular population. The term is used mostly in connection with national population and housing censuses; other common...
respondents sometimes inaccurately report ages or dates of birth. Whipple's index (index of concentration), invented by the American demographer George Chandler Whipple (1866–1924), indicates the extent to which age data show systematic heaping on certain ages as a result of digit preference or rounding
Rounding
Rounding a numerical value means replacing it by another value that is approximately equal but has a shorter, simpler, or more explicit representation; for example, replacing $23.4476 with $23.45, or the fraction 312/937 with 1/3, or the expression √2 with 1.414.Rounding is often done on purpose to...
. Typically the concern is for heaping on particular ages such as those ending in 0 and 5.
The Whipple index score is the five times the percentage of persons in the age range 23–62 inclusive, who report ages ending in 0 and 5. 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
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...
recommends a standard for measuring the age heaping using Whipple's Index as follows:
| Whipple's Index | Quality of Data | Deviation from Perfect |
|---|---|---|
| < 105 | very accurate | < 5% |
| 105–110 | relatively accurate | 5–9.99% |
| 110–125 | OK | 10–24.99% |
| 125–175 | bad | 25–74.99% |
| > 175 | very bad | ≥ 75% |
Applicability
Whipple's index applies to digit-preference in 5- and 10-year intervals. While other measures of age heaping, such as Myer's Blended Index, can be applied to find preferences for any terminal digit, the patterns of heaping may be complex.For example, it has been shown that among Han Chinese
Han Chinese
Han Chinese are an ethnic group native to China and are the largest single ethnic group in the world.Han Chinese constitute about 92% of the population of the People's Republic of China , 98% of the population of the Republic of China , 78% of the population of Singapore, and about 20% of the...
, age heaping occurs on a 12-year cycle, consistent with preferred animal years of the Chinese calendar
Chinese calendar
The Chinese calendar is a lunisolar calendar, incorporating elements of a lunar calendar with those of a solar calendar. It is not exclusive to China, but followed by many other Asian cultures as well...
. 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
Turkic peoples
The Turkic peoples are peoples residing in northern, central and western Asia, southern Siberia and northwestern China and parts of eastern Europe. They speak languages belonging to the Turkic language family. They share, to varying degrees, certain cultural traits and historical backgrounds...
Muslim populations in China (Uyghurs
Uyghur people
The Uyghur are a Turkic ethnic group living in Eastern and Central Asia. Today, Uyghurs live primarily in the Xinjiang Uyghur Autonomous Region in the People's Republic of China...
and Kazakhs
Kazakhs
The Kazakhs are a Turkic people of the northern parts of Central Asia ....
in Xinjiang
Xinjiang
Xinjiang is an autonomous region of the People's Republic of China. It is the largest Chinese administrative division and spans over 1.6 million km2...
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
Dragon (zodiac)
The Dragon , is one of the 12-year cycle of animals which appear in the Chinese zodiac related to the Chinese calendar, and the only animal that is legendary...
. But among Turkic Muslims, heaping was found at ages 35, 40, 45, 50, 55, 60, and so on and increased in magnitude with age.