Workshop on Demographic Analysis and Evaluation 1 Age

Workshop on Demographic Analysis and Evaluation 1

Age and Sex Structure: Evaluation 2

Population Age-Sex Structure In this part of the workshop you will learn that Age and sex structure is a map of a population’s demographic history. Knowledge of age structure is essential to the analysis of fertility, mortality, and migration. Errors in the distribution of a population by age and sex are replicated and repeated in population projections. 3

Population Age-Sex Structure We will also discuss Sources of age data Tools for evaluating the quality of age-sex data Tools for adjusting or correcting for possible errors in age-sex data 4

Population Age-Sex Structure: Introduction This discussion follows Chapter 2 of the Census Bureau’s Population Analysis with Microcomputers. The importance of age-sex composition, techniques for evaluation of age-sex data, and methods for correcting age-sex data are discussed in more detail in Chapter 2. 5

Population Age-Sex Structure: Introduction The distribution of a population by age and sex is one of the most basic types of information needed in planning for the future. Any analysis of educational requirements, military needs, labor force projections, family composition, retirement, migration, or voting practices, for example, would not be complete without considering information on age. Age is a crucial component in demographic analysis as well. The study of mortality and fertility without considering age will permit only a partial understanding of these phenomena. 6

Population Age-Sex Structure: Introduction Given the importance of the age structure with respect to social and economic characteristics, it is imperative that the information on the population age and sex structure be as accurate as possible. The following discussion covers the graphic presentation, evaluation, and adjustment of data on age. 7

Age Structure as a View of the Past A population's age structure may be considered as a map of its demographic history. Persons of the same age constitute a cohort of people who were born during the same year (or period); they have been exposed to similar historical events and conditions in the nation. The age structure of the whole population at a given moment may be viewed as an aggregation of cohorts born in different years. 8

Age Structure as a View of the Past A graphic representation of the age structure of the population, such as an "age pyramid, “ shows the different surviving cohorts of people of each sex in the country. 9

ple who were born during the same year (or period); they have been exposed to similar historical facts and conditions in the nation. The age structure of the whole Age Structure as a View of the Past A pyramid for a country affected by substantial historical changes in fertility and mortality. 10

ple who were born during the same year (or period); they have been exposed to similar historical facts and conditions in the nation. The age structure of the whole Age Structure as a View of the Past The age structure of a population is affected by migration as well as by fertility and mortality. For some countries, the impact of net international migration is substantial 11

Age Structure as a View of the Past Baby bust during famine, 1958 -60 “Echo” Fertility restrictions starting early 1970 s Source: International Data Base, U. S. Census Bureau 12

Age Structure as a View of the Past “Echo” Smaller cohorts 25 years later Source: International Data Base, U. S. Census Bureau 13

Age Structure as a View of the Past This cohort in Vietnam was born between 1940 and 1949. The cohort is constricted for several reasons: Baby bust during WWII War casualties in late 1960 and early 1970 s High outmigration in the cohort following 1975 reunification 14 14

Age Structure as a Snapshot of the Present 15

Age Structure as a Snapshot of the Present 16

Checking Census Data for Consistency Comparing historical population age distributions for a country helps in analyzing data consistency. This may be accomplished graphically by plotting the population in the various age groups by year of birth. Such a figure reveals past trends of fertility, migration, age misreporting, and even errors in census enumeration. The graph cannot disentangle actual demographic history from statistical errors, but it can indicate in general whether the age distribution is acceptable as reported or if it needs some adjustment. 17

Graphical Methods for Checking for Age Misreporting 18

Methods of Checking for Age Misreporting Age misreporting, which may arise from error on the part of the respondent or from misestimation of age by the interviewer, may be suggested by irregularities evident in indices or graphs. Population pyramid by single years of age Age and sex ratios Cohort comparison Summary indices of “irregularities” in age structure or in age-sex structure Spreadsheets: PYRAMID SINGAGE AGESEX GRPOP-YB 19

Indices Used to Identify Digit Prefernce There are several frequently used indices for detecting digit preference: Myers (1940), Whipple (U. S. Bureau of the Census, 1971), Bachi (1951, 1953), Carrier (1959), and Ramachandran (U. S. Bureau of the Census, 1971). These indices not only provide an overall idea of the extent of age misreporting but also indicate the preference for certain ending age digits. However, the analysis can be done graphically by constructing a typical population pyramid by single years of age. 20

Other Methods of Checking for Age Misreporting 21

Indices of Mis-reporting: Digit Preference – SINGAGE. xls Spreadsheet: SINGAGE 22

Indices of Mis-reporting: Digit Preference – SINGAGE. xls 23

Other Methods of Checking: Age Ratios An age ratio is defined as: 5 Px 5 ARx = 100 1/2 (5 Px-5 + 5 Px+5) Where 5 ARx represents the age ratio for ages x to x+4; and 5 Px represents the population at ages x to x+4. 24

Possible Indices of Mis-reporting: Age Ratios If fertility and mortality have not fluctuated much in the past and international migration has not been significant, the “walls” of the population pyramid should be fairly smooth. In such case, age ratios should be fairly close to 100. Source: International Data Base, U. S. Census Bureau 25

Possible Indices of Mis-reporting: Age Ratios If fertility and mortality have not fluctuated much in the past and international migration has not been significant, the “walls” of the population pyramid should be fairly smooth. In such case, age ratios should be fairly close to 100. Source: International Data Base, U. S. Census Bureau 26

Possible Indices of Mis-reporting: Age Ratios If fertility and mortality have not fluctuated much in the past and international migration has not been significant, the “walls” of the population pyramid should be fairly smooth. In such case, age ratios should be fairly close to 100. Smooth Walls Fluctuating Walls Source: International Data Base, U. S. Census Bureau 27

Possible Indices of Mis-reporting: Age Ratios Caution – Fluctuating age ratios across the age spectrum do not necessarily indicate reporting problems. For instance, if fertility actually has fluctuated over time, the shifting age ratios may reflect actual historical realities (as we saw earlier for China and other countries). Source: International Data Base, U. S. Census Bureau 28

Other Methods of Checking: Age Ratios (1960 census, apparent age misreporting) (pyramid, small past changes in fertility) 29

Other Methods of Checking: Sex Ratios A sex ratio at a given age may be defined as: 5 MPx 5 SRx = 100 5 FPx Where represents the sex ratio at ages x to x+4; and 5 SRx 5 MPx and 5 FPx represent the male and female populations, respectively, at ages x to x+4. 30

Other Methods of Checking: Sex Ratios As in the case of age ratios, the larger the abrupt departure of this ratio from values close to 100, the larger the possibility of errors in the data. The level of the sex ratios depends on the number of male and female births and on the mortality of the population. All populations have more male than female births, and so the sex ratio at the early ages is expected to be slightly over 100 (103 to 106). However, since mortality is usually higher for males than females, the sex ratio is reduced continuously up to the oldest ages. 31

Other Methods of Checking: Sex Ratios 32

Possible Indices of Mis-reporting: Sex Ratios Example of reported sex ratios by 5 -year age groups “Model” pattern of sex ratios by age 33

Other Methods: The Age-Sex Accuracy Index In the early 1950 s, the United Nations suggested a joint accuracy index to summarize the values of the age and sex ratios. The sex-ratio score (SRS) was defined as: The mean difference between sex ratios for the successive age groups, averaged irrespective of sign. The age-ratio score (ARS) was defined as: The mean deviation of the age ratios from 100 percent, also irrespective of sign. 34

Other Methods: The Age-Sex Accuracy Index Based on empirical relationships between the sex-ratio scores and the age-ratio scores, the following index was defined as the joint score (JS) or age-sex accuracy index: JS = 3 x. SRS + ARSM + ARSF Where ARSM is the age-ratio score for males ARSF is the age-ratio score for females Spreadsheet: AGESEX 35

Other Methods: The Age-Sex Accuracy Index Based on empirical analysis of the age and sex declaration in censuses from different developed and developing countries, the United Nations suggested that the age and sex structure of a population will be (a) accurate if the joint score index is under 20, (b) inaccurate if the joint score index is between 20 and 40, and (c) highly inaccurate if the index value is over 40. These indices are useful mainly in international or historical comparative analyses. 36

Census Errors vs. Actual Demographic Change To distinguish reporting problems from actual demographic change, here are some common patterns to look for in successive censuses: Observation Possible Explanation 1. Consistent dips/bumps among cohorts 2. Unique changes in particular cohorts 3. Consistent dips/bumps across ages • May indicate true change in fertility • May indicate true immigration • May indicate age misreporting 37

1. Consistent Dips/Bumps among Cohorts Successive census counts all suggest a dip in the cohort born in the 1930 s. Cohort “A, ” born was aged: 20 -29 in 1960 census, 30 -39 in 1970 census, 40 -49 in 1980 census. The consistency of the dip (counted at different age groups) likely suggests that this cohort was the product of a temporary baby bust. 38

2. Unique Changes in Particular Cohorts The data points from A through B indicate a cohort of persons born between 1926 and 1965 who were 15 to 54 years of age at the time of the 1980 census; this cohort is larger than it was when enumerated in the 1975 census. 39

3. Consistent Dips/Bumps across Ages 10 -19 show a dip relative to adjacent age groups in both censuses A shortage of people in ages 10 to 19 years in the 1960 census (C and D) is repeated at the same ages in the 1970 census (A and B). Ages 55 -59 show a dip relative to adjacent age groups in both censuses The same situation appears in the older ages (points H, I and J repeated in points E, F, and G). Spreadsheet: GRPOP-YB 40