BACKGROUND: Data on age in developing countries are subject to errors, particularly in circumstances
where literacy levels are not high. A common error in age reporting is the tendency of rounding the ages
to the nearest figure ending in ‘0’ or ‘5’ or to a lesser extent, to the nearest even number. Because of this
tendency, commonly known as “digital preference”, age heaping occurs at certain ages.
The aim of this study was to study this phenomenon and both Myers’ and Whipple’s Indexes were
employed to identify the digit preference in Iranian national census, 2005.
METHODS: Myers’ and Whipple’s Indexes were employed to study the pattern of digit preference. The
Myers' Blended Index shows heaping at ages ending in 0 and 5 years, and the pattern of heaping is pronounced
for both urban and rural populations.
RESULTS: The quality of age reporting for the 2005 census data was poor if compared to the 1995 census
data. Digit preference occurred most often in the female population compared to male one, and in rural
areas compared to urban ones.
CONCLUSIONS: It can be concluded that both males and females tend to misreport their ages before age
60 especially in rural areas. So, whenever any data gathering regarding age information occurs, the ID
card should be used regardless of person's self report.