Assessment and appraisal of the 2019 Census results

To have a solid basis for publishing the results of the 2019 Census, contributing to consolidating user beliefs and understanding of the collected data, the Central Steering Committee conducted a post-enumeration survey⁹ for the 2019 Census immediately after completing EA data collection. In addition, UNFPA assisted by sending an international expert to Viet Nam to conduct an objective assessment of the quality of the Census data in the first 10 days of August 2019. Some results of the 2019 census data quality assessment are as follows.

3.1.1. Population size

The Population and Housing Census in Viet Nam determined population size based on concept of usual residents (de jure). The results show that total population of Viet Nam at the time-point 00:00 on 1 April 2019 was 96.2 million persons.

The post enumeration survey was used to determine the coverage error (defining the completeness of the Census), so each usual resident in the post enumeration areas was interviewed with 4 questions: (1) full name; (2) relationship to household head; (3) sex; and (4) month and year of birth or rounded age. Information gathered from these questions during the post-enumeration survey was compared with the Census results to find cases of duplication or omission in the Census.

The results of the post-enumeration survey showed that the net coverage error of the Census was 0.2%, equivalent to about 143,000 persons, an acceptable threshold. Compared to the error rate of 1.5%-4.5% of the total population, commonly found in the Population and Housing Censuses of other countries, the completeness of the 2019 Census of Viet Nam was quite high.

Table 3.1: The results of the post enumeration survey on the 2019 Population and Housing Census

Unit: % Duplication rates Omission rates Net coverage error

(Omission - Duplication)

ENTIRE COUNTRY 3.4 3.6 0.2

Northern midlands and mountain areas 3.2 2.4 -0.8

Red River Delta 2.3 2.9 0.6

North Central and Central coastal areas 2.9 2.3 -0.6

Central Highlands 4.1 5.4 1.3

South East 3.0 3.9 0.9

Mekong River Delta 5.6 6.0 0.4

9 Post enumeration survey of the 2019 Population and Housing Census was conducted in May 2019 in accordance with Plan No.31/KH-BCDTW dated 27 March 2019 at 70 EAs in 63 provinces and cities directly under the Central Government.

4242 | / RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019 The total population from the 2019 Census was close to the mid-2019 population estimate from the Population Division of the United Nations published in “World Population Prospects 2019”

at 96.5 million inhabitants. In addition, the 2019 Census total population figure was between the estimates for the medium fertility variant (95.4 million) and the high fertility variant (97.6 million), which were generated from the “population projections” report prepared by the GSO in 2010 following the 2009 Census.

Thus, the 2019 Census population total result proved very close to statistical expectations from both internal and external sources, again confirming the overall quality of the 2019 Census.

3.1.2. Age and sex distribution

Analysis of population size by single year of age, five-year age group, sex and regions between the 2009 Census and 2019 Census, as well as age distribution from the 2014 Intercensal Population Survey, confirmed the 2019 Census age information quality.

However, there were significant variations in population structure between five-year age groups from the 2009 and 2019 Census: the successive peaks and troughs around ages 5-30 from the 2019 Census are simply a legacy of past variations in the size of birth cohorts from the results of the 2009 Census. These variations in birth cohort size were caused by successive episodes in Viet Nam’s recent demographic history: war mortality, the post-war recovery (which recorded a “baby boom”), the subsequent rapid fertility decline caused by population policy and the later “baby echo”

when the baby boomers gave birth at reproductive age from 2005 onwards. The curve in 2009 bias to the last 10 years had a tendency of similarity to the curve in 2019. In other words, the comparison with the 2009 age distribution showed that both curves had identical shapes with a ten-year gap.

Figure 3.1: Structure of population by age group, 2009-2019

Unit: %

0%

2%

4%

6%

8%

10%

12%

2009 2019

0 2 4 6 8 10 12

2009 2019

Age group

RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019 RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019 / 43| 43 The following figure depicts the age structure of 5-year birth cohorts by sex; the population structure by age group was identical in both males and females. There was a higher sex ratio than expected below age 20 in males and females linked to sex imbalances at birth in Viet Nam over the last two decades. The lower sex ratio than expected from age 50 onwards in males and females could possibly be linked to excess male (war-related) mortality in the past.

Figure 3.2: Differentials in sex by age group from the 2019 Census results

Unit: %

3.1.3. Assessment of quality of age information

Although there were very strict regulations in collecting age-related information, there were discrepancies between gathered information and reality, for many different reasons. Common errors in age reporting included respondents not correctly remembering their age or the age of other family members, respondents choosing to report a more socially desirable age and respondents choosing lucky numbers. Some respondents round their age to end in 0 or 5. These inaccuracies can lead to abnormal population concentrations in preferred ages, and underrepresentation in unpopular ages, ultimately distorting data on population distribution by age.

According to United Nations recommendations, three indices are often used to assess the quality of age information in population statistical surveys: Whipple’s index, Myers’ index and the UNI index.

The Whipple’s index is used to measure preferences for ages ending in 0 and 5. This index’s value ranges from 100 to 500: 100 or less indicates no preference for ages ending in 0 and 5;

conversely, a Whipple’s index of 500 would indicate all respondents declared their age ended in a 0 or a 5.

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

Males Females

0 1 2 3 4 5 6 7 8 9 10

Males Female

Age group

44 / RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019 44 | RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019

The Myers’ index is used to measure preferences or dislikes for ages ending in each digit from 0 to 9. In theory, a Myers’ index of 0 would signify a normal age distribution. An index of 90 would indicate all recorded ages ended in the same digit.

The UNI index (United Nations Age-Sex Accuracy Index) evaluates the quality of reported age-sex distributions in five-year age groups. Age declaration accuracy is measured using average survey age ratios; a UNI value under 20 is accurate; between 20 and 40 is not accurate and over 40 is very inaccurate.

These three indices had better results in the 2019 Census than the 2009 Census. The results of the Whipple’s, Myers’ and UNI index from the 2019 Census data showed that the age declaration of households did not concentrate or prefer at a certain age, and the Age-Sex accuracy index of the population was better than the results of the 2009 Census. Detailed results of the three indices in 2009 and 2019 are presented in the following Table.

Table 3.2: Indices assessing the quality of information on age in the Census, 2009-2019

2009 2019

Age heaping index (Whipple) 100.4 100.1

Index of age preference (Myers) 1.72 1.38

Age-sex accuracy index (UNI) 28.4 26.1

3.1.4. Information on migration

The net migration ratio by region in the 5 years prior to the 2019 Census corresponds to the difference between the actual population growth rate and the natural regional population growth rate from 2015-2019. This illuminated immigration realities in localities where production developed and was in high need of human resources.

3.1.5. Number of deceased

The aggregated number of those deceased in the last 12 months before the 2019 Census suggests there was an underreporting in the number of deaths, although the age distribution of the deceased was relatively consistent with the projected death model. However, more cases of male deaths were recorded than female deaths. The number of estimated cases of death from the 2019 Census results were smaller than the number of estimated cases of death from the results of the Annual Population change survey. Thus, it is worth considering a more appropriate estimated death model for Viet Nam to compile related indicators.

RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019 RESULTS - THE VIET NAM POPULATION AND HOUSING CENSUS OF 00:00 HOURS ON 1 APRIL 2019 / 45| 45 3.1.6. Missing errors

The 2019 Census applied advanced IT during EA data collection with 99.95% of households surveyed using CAPI questionnaires and Webforms. The electronic questionnaire used a friendly design with appropriate logic check steps that contributed towards improving the quality of survey data. The number of data fields missing information in the 2019 Census decreased in comparison with the 2009 Census.

Table 3.3: Number of data fields missing information of the Census, 2009-2019

Unit: Case

2009 2019

Relationship to household head 67 6

Ethnic group 41 3

Religion 2,753 37

School attendance 4,789 2,282

In short, a data quality assessment of the 2019 Census indicates that data collection using CAPI programs saved Census time and sources and improved information quality. There was no direct or indirect evidence yielding negative impacts on the quality of the Census data as a result of applying CAPI.