Sample survey methodology

The rural and city surveys were based on probability samples. First, the sampling plan and methodology of the rural surveys are described. As the sampling designs of the two rounds of National Sample Surveys, 1964-67 and 1968-71, are similar, the design of the second round only is described-^. A stratified two-stage sampling design was adopted for the National Sample Survey, second round. The 450 rural districts of the country (excluding Eritrea and the nomadic areas) formed the first level of stratification. Within each district, a complete list of all the administrative subdivisions was prepared to serve as the first stage sampling frame. In the case of districts with less than 30 subdivisions, the first stage sampling consisted of selecting two subdivisions with probability proportional to size; size being their administrative population counts or some other

^ S O , 1980a.

3The methodology of the National Sample Survey Second Round is described in the report CSO, 1974a: 123-130.

suitable measure of size if available, otherwise with equal probability. If there are more than 30 subdivisions, two pairs of contiguous subdivisions were selected, by selecting two nucleus subdivisions with probability proportional to size, and then selecting a neighbouring subdivision for each nucleus with equal probability among all its contiguous neighbours. The second stage sampling consisted of listing all households in the selected subdivision and then making a systematic selection of households for further inquiries such that the overall sampling fraction is 1 in 100. In the case of the first round National Sample Survey, the overall sampling fraction varied from 0.5 to 2 per cent. The field staff, enumerators and supervisors, of the Central Statistical Office did the fieldwork of these National Sample Surveys.

The scope of the 1968-71 National Sample Survey was to cover all the settled rural areas, where survey work was feasible, excluding the nomadic areas. However, not only was the nomadic population excluded, but so also were the population of Eritrea and some provinces within the covered regions. As a whole, the 1968-71 Survey covered 82 per cent of all the districts (CSO, 1974a: 123-125). The coverage of the 1964-67 National Sample Survey first round was similar. At that time separate estimates could not be obtained for Bale as it was part of Harerge region, and so there are no separate data for Bale in the first round as in the latter surveys.

The objectives of the 1980-81 Demographic Survey included: estimation of national and regional population size and composition; estimation of various population characteristics such as age structure, marital status, ethnic and religious group, literacy and educational level; and estimation of fertility, mortality and migration (CSO, 1980b: 1). The Demographic Survey was a two round Survey, the first conducted in January 1981 and the second in January 1982. The 1980-81 Demographic Survey, first round, is the source of this study and is described in the following.

The sampling plan was developed to meet the objectives of the Survey. The 1980-81 Demographic Survey was a stratified two-stage sample design; the stratification being at the level of the province4. A list of Farmers’ Association Areas (FAs) was compiled within each province, and then FAs were selected as primary sampling units without replacement using probability proportional to total members of respective FAs; 500 FAs were selected (for the meaning of Farmers’ Association Area, see last paragraph of Subsection 1.5.2). Within each selected FA, 100 households were randomly selected

4The sample design and estimation procedure and estimates o f sampling errors are given in the publication CSO, 1985: Appendix 1.

from lists of households generated after the selected FAs were identified. The Survey actually covered 477 FAs and 46,307 households in 419 agriculturally important districts (CSO, 1985a: i). The Survey covered all regions except Eritrea and Tigray. It also excluded the nomadic population.

The fieldwork for the 1980-81 Demographic Survey was conducted by 500 resident contract enumerators recruited by the Central Statistical Office to collect data for the surveys that made up the Rural Integrated Household Survey Program of which the Demographic Survey formed an integral part. The other components of the Program include multi-round surveys on agriculture, household income and expenditure, labour force, health and nutrition, etc. The enumerators, who were mostly high school graduates, were recruited from their regions for language and familiarity with culture. They were given two weeks training on concepts, how to conduct interviews and fill in the questionnaires and practicals for both the Agricultural and Demographic Surveys which constituted the first two surveys of the Program. The questionnaire and enumerators’ instruction manual were in English. As these two constituted the initial surveys of the Program, considerable efforts were made to ensure data quality through adequate training, quality control through field supervisors, staff field supervision, and manual and computer editing at the Head Office.

The scope and coverage of all the rural surveys were similar. There is no quantitative demographic information on Eritrea and the nomadic population because of then- exclusion from these surveys owing to security problems in Eritrea since the 1964-67 Sample Survey, and to both security and survey difficulties in the nomadic areas. Tigray was also not covered in the 1980-81 Demographic Survey for security reasons, but unlike Eritrea and the nomadic areas, data exist for Tigray from the two rounds of National

Sample Surveys (see Figure 4.1 for a map and note on the coverage of the surveys).

The 1967 Population Sample Survey of Addis Ababa immediately followed the September 1967 Housing Census of the city, and was designed to collect detailed demographic information. For the Population Sample Survey, a 10 per cent systematic sample of enumeration areas was selected with a random start from the census list of the 900 enumeration areas arranged according to the 10 districts of the city. All households within the selected enumeration areas were enumerated (see Central Statistical Office,

1972, Apendix 1).

The 1978 Addis Ababa Demographic Survey immediately followed the August 1978 Housing Registration. For the purpose of the Housing Registration, the city was divided

into 1,060 enumeration areas, which were stratified by Higher Urban Dwellers’ Associations (Keftegnas), 25 in number, and constituted the sampling frame. A group of

Kebeles makeup a Keftegnas (for the definition of Kebele, see last paragraph of

Subsection 1.5.2). A stratified single-stage cluster sampling was adopted for the Demographic Survey and 80 enumeration areas were selected. All households were surveyed in each selected enumeration area: a total of 20,357 households which represented eight per cent of all households in the city (Central Statistical Office, 1979: 3). The Survey was designed to produce reliable estimates of demographic parameters at the city level.

The 1984 Addis Ababa Population and Housing Census was part of the first-ever Population and Housing Census of Ethiopia; it covered all persons in private households and institutions, and also the homeless population. The objectives of the census among other things were to establish the levels of fertility, mortality and migration. The Census combined both de jure and de facto methods of enumeration. The census reference date was the night of 9 May 1984 and enumeration continued for about two weeks. To ensure complete coverage of households and areas, census cartographic work was undertaken to divide the city into enumeration areas (EAs) consisting of 150-200 households, and EA maps were prepared; as a result, the city was delineated in 1,517 EAs. The census procedure consisted of EA identification by the enumerator with the help of the EA map and officials of the area; listing of all households, housing units and establishments in the EA; and then completing the Population and Housing Census questionnaire by canvassing every household within the EA (Office of the Population and Housing Census Commission, 1984: 12). Each EA was assigned to an enumerator who was expected to complete the enumeration in two weeks, and who usually was a senior high school student or graduate and was given a week’s training. The language of the Population Census questionnaire and documents was Amharic, the official language, unlike that of the previous surveys which was English.

The subset data of the 1984 Addis Ababa Population Census prepared by myself is a representative cluster sample of 25 EAs selected from the 1,517 census EAs. These cluster EAs were selected to reflect if there are any socio-economic differentials between the different residential sectors of the city, in this case the 25 Higher Urban Dwellers’ Associations (HUDAs) that makeup the city. The EAs were first stratified according to their distribution by the 25 HUDAs. Then one EA was randomly selected from every HUDA with equal probability of selection. The subset data used here are not weighted. The data relating to all persons and households within the selected EAs comprise the

subset data of this study. The 25 sampled EAs comprise 22,655 persons living in 4,370 households. This subset sample represents 1.6 per cent of the city’s census population. The subset data contain characteristics of 5,805 women of reproductive age.