Sampling Procedure
Sampling Frame
The 2002 population and housing census provided a frame for sample selection. The frame contains a list of all administrative units up to the lowest level called, 'Local Council 1', or LC1. This is usually, but not always consistent with a village in terms of area. The Enumeration Area (EA) may comprise of one village/LC1, or more than one village/LC1. The demarcation of EAs is based on total population within a given area and in many instances, may vary by locality. In addition the sampling frame also indicates the EA to which a particular LC belongs. The 2002 Uganda Sampling Frame has a total of 33,283 EAs.
Study population
The study population comprised of the entire population of Uganda. Based on the distribution of households in table 1 above, the sample was determined based on information from Uganda National Household survey 2005/06 conducted by the Uganda Bureau of Statistics. The proportion of internal migrants reported in the past 5 years has been used to estimate the required sample. Given the limited nature of the number of international migrants, the proportion of internal migrants is considered adequate to provide sufficient estimates of the indicators of interest.
Sample allocation by region
The above sample was proportionately allocated across the four statistical regions on the basis of the population in each of the regions. There was oversampling for urban population approximately by 5 times. To ease implementation, the regional sample was further disaggregated down to Enumeration Area level.
Selection of Enumeration Areas
The task was to undertake a nationally-representative survey of 2,000 households (urban and rural combined) in 2009 that would provide information on migration, remittances and their effects on development.
The frame was be divided into two strata namely rural and urban. A two-stage stratified sample design was adopted. The first stage representing the primary sampling unit comprised of the selection of EAs from each of the strata while at the second and ultimate stage households were selected. EAs were selected from the list of Enumeration Areas developed after the 2002 Population and Housing Census and updated to include new districts.
The selection of EAs was proportionally done based on the number of households in the respective stratum according to the 2006 Uganda household survey. All the EAs in each domain were sorted by county, sub-county and parish. A random number was generated and an appropriate random start and sampling interval was systematically selected from the ordered list with probability proportionate to number of households. This was done separately for urban and rural areas, hence stratified sampling. The proportion of EAs sampled in urban areas is about 5 times that in rural.
Selection of households
At the second stage, a complete listing of households in each EA was done to classify the households into three groups: non migrants, internal migrants and international migrants. The number of households per EA varied from around 20 to about 1000. Most of the time, all households were listed even in the large EAs since it was difficult to establish lines of demarcation to segment the EA.
A total of 10 households were selected randomly from each of the 200 EAs. The goal was to select 4 households with an international migrant (emigrant), 3 with one or more internal migrants, and 3 with no migrant. This sampling was done from the three strata or listings of households according to migration status. Separate sampling was done from each stratum using systematic sampling. In case of a refusal or other reason for non-response, another household was selected from the same stratum to reach the desired quota. In case the number of households listed in any of the three strata was smaller than the numbers desired (4, 3, 3), then all those listed in that stratum were automatically sampled and the short fall selected from the next stratum.
For example, if there were, say, 150 households in an EA, with 3 with international migrants, 27 with internal migrants, and 120 with no migrants, the numbers selected would be, respectively, 3, 3 and 3. But to make up 10, priority would be given to the migrant stratum to add one more, randomly selected, from that stratum. As another example, suppose there were 0 international migrant households; then 7 would be selected from the internal migrant stratum and still only 3 from the list of non-migrant households.
The choice of 10 households per EA was based on experience from the various economic surveys conducted by UBOS, where 10 households provide adequate representation at EA level for most of the economic and social indicators.
The listing operation
The survey targeted household with in-migrants or former members who have migrated away, whether to another part of the country (urban or rural) or to another country. Since the census frame does not uniquely identify who is a migrant or non migrant, and owing to the lack of an up to date list of all households in Uganda from which to draw the sample, the survey team adopted a listing exercise as stop gap measure.
The exercise involved conducting a fresh listing of all households in each of the selected EAs. During the exercise, households with migrants were identified and the migrants clearly categorized as internal-within Uganda- or international where household members had moved to another country all together. The total number of listed household numbers was 24,618. Thereafter, a sample of 10 households was selected using systematic sampling procedure.