Reasons for Age Misreporting

Several reasons for age misreporting exist. Therefore, the individual reasons for the misreporting have to be taken into account, when approximating education by age misstatements. Errors in data processing, for example typos, problems when deciphering the handwriting of the inter-viewers, or erroneous classication in a dierent age group are a potential source of error. But these errors introduced by the interviewers or persons that analyze the census material are likely to cancel each other out (Ewbank 1981, p. 13-15). Miscommunication between interviewers and interviewees can also lead to biased age data (Oppenheim Mason and Cope 1987). Such errors, however, are subject to all data which is obtained from interviews. Therefore, we will not put much emphasis on these reasons, but rather review reasons which are especially important when studying age data; specically the errors that emerge from intentional or unintentional age misreporting.

2.3.1 Ignorance of the Own Age

The ignorance of one's own age is the most likely source of age misreporting. Especially in societies in which birth documents are not common, people may lack the knowledge of their age.

In agricultural societies or societies in which the birthday is not celebrated, the knowledge about the own age is of subordinate importance. People in these societies orient themselves mainly to the change of harvest periods, historical events, or natural disasters. Men in Morocco in the 1960s, for instance, were often not able to report their age, but knew the number of Ramadans they had celebrated. This information helped census takers then to calculate the age (Scott and Sabagh 1970). The other way around, birth certicates used to compile census data or used to infer about the age of the interviewees will dilute heaping patterns in age data, although the respondents were unsure about their true age.

2.3.2 Economic and Social Factors

Factors that involve the preference or avoidance of certain ages due to personal, economic, or social reasons are a further important source of age misstatements. Budd and Guinnane (1991) nd that the pensions act, that granted a pension for all British subjects aged 70 or older, induced a share of the Irish population to state an age older than 69. Similarly, men may try to avoid the military service by stating a younger age.

2.3.3 Cultural Factors

Cultural factors of age misreporting are essential. Single women, for instance, might tend to understate their age to have better possibilities on the marriage market (Ewbank 1981). Are certain cultures less prone to heap their ages? Cultures in which the year of birth is of exceptional importance may show less pronounced age heaping patterns. In China, for instance, a high share of the population in the 18^thand 19^th century was able to state the age correctly (Baten et al. 2008). The lunar calendar allowed interviewers to calculate the respondent's age relatively accurate, while the conversion from the lunar to the Western calendar may have caused distortions in the age data of past censuses. Minorities which do not use the lunar calendar generally show higher age heaping patterns (Coale and Li 1991, Jowett and Li 1992). For China in the late 20

th century, Jowett and Li (1992) nd no correlation between age accuracy and literacy due to the non-existing age-heaping in the Chinese data. State demand for age reporting in form of an extremely long history of census taking may also lead to lower age heaping levels (Crayen and Baten 2009a). Thomas (1987) states that numerical abilities may be higher in societies in which trade plays an important role. Everybody involved in trade had to calculate and therefore, arithmetic as 'the very soul of trade'(Hodden cited in Thomas 1987, p. 107) may lead to an improvement in numerical abilities.

2.3.4 Proxy Respondents

In certain cases, not the person itself answers the questions of the census takers, but proxy respondents, like neighbors. These are less likely to know the exact age of others and may therefore report an estimated age (West, Robinson, and Bentley 2004). The problem of proxy

respondents is addressed more thoroughly in Chapter 4. In general, the interviewers in the Latin American population counts had the instruction to ask each person individually and therefore biases from this source are likely to be small.

2.3.5 Old Ages

Besides the eect that older people received less education and are therefore more prone to report rounded ages, very old people have a higher propensity to give a wrong age because they tend to exaggerate their age. Del Popolo (2000) studies age misreporting among older age groups in Latin American population counts and nds a strong positive correlation between the degree of age heaping and the share of ancient people. A higher age means a higher social reputation.

Thus, lower age awareness in a society leads to stronger age exaggeration among the oldest age groups. Kestenbaum (1992) concludes that the problems are especially serious for people aged 95 or older, while del Popolo (2000) nds important eects for the population older than 60 in the less developed Latin American countries and 80 in the more developed countries. A good example for age exaggeration is ancient Rome. Although life expectancy at birth was only around 20 to 25 years, the tombstones show people that died at age 120 (Clark 2007, p. 178). Age statements of older people have therefore to be treated with care. For this reason, we excluded the oldest age groups from our analysis in the following chapters.

2.3.6 Coverage Errors

Under- or over-enumeration of individuals may cause errors in certain age ranges. Migration or the formation of households is the most important factor leading to underenumeration. Engaged women who are still living in their parent's home are often not counted as belonging to their parent's household, but are neither counted in their future spouse's. Similarly, marginal members of households like servants or nonrelatives may not be counted (Ewbank 1981, p. 60).