Sampling

THE MCH SURVEY

4.2 Sampling

The study design used for the MCH survey was a cross-sectional analytical community- based survey. A community-based study was appropriate as it included all people in the study area including those not regularly attending the PHC clinics.

4.2.1 Sampling of clinics

Purposive sampling was used to select a cluster of five neighbouring fixed PHC clinics with their catchment populations based on documented usage patterns. These five clinics were selected from an area where there were few mobile clinic points and hospitals adjacent to their boundaries that might introduce facility selection bias or confound the results. The five clinics were selected from the southern part of the Umkhanyakude District between Bethesda and Mseleni hospitals in Ubombo magisterial district (see Figure 3.1). The five clinics selected were Madonela, Makhathini, Ophansi, Ntshongwe and Mbazwana. All five clinics offered a similar range and standard of PHC services namely, well-baby care, antenatal care, maternity services, family planning, chronic illness care and treatment of minor ailments (see Appendix 2).

4.2.2 Generation of distance buffers around PHC clinics and sampling of homesteads

This section provides a basis for random sampling of homesteads in the MCH survey and for analysis of the relationship between accessibility and a number of indicators collected as part of the MCH survey. The creation of distance buffers around clinics directly served the sampling and the analytical needs of the MCH survey. The technique involved generation of 1 km distance buffers around each clinic within a smaller sample of five neighbouring fixed PHC clinics selected above.

The sampling units were homesteads within catchment areas based on usage for these clinics. A data file was created from catchment areas based on usage for each of the five designated clinics. Each of these files was opened separately in MapInfo® GIS software to spatially display the clinic and its catchment population. 1 km distance buffers were created around the clinics using the Object and Buffer menus of MapInfo® (Figure 4.1).

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After the generation of distance buffers for each of the five clinics, the data were saved into a file for each clinic and imported into MS Access and then SPSS statistical package for sampling purposes. A stratified random sampling was used to select an approximately 10% representative sample of homesteads from each 1 km buffer in catchment areas for each of the five selected clinics. This resulted in a sample size of 685 homesteads selected from a total of 6 665 homesteads (42 256 population). This sample size was considered to have sufficient power (90%) to determine significant differences between indicators of MCH service utilization and health status at different distances from the clinic with 95% confidence.

4.2.3 Selection of mother-child pairs

Lists for the 685 sampled homesteads were generated for use during the MCH survey to identify mother-child pairs in the study area. These lists contained data on the homestead owner, area, section, and homestead number. These data enabled the fieldworkers to identify the homesteads during the fieldwork. The respondents sampled for the MCH survey were mothers of children aged 12-23 months who were resident in Ubombo magisterial district during the study period. The presence of children aged 12- 23 months irrespective of whether the biological mother is alive or deceased, was therefore the primary selection criterion in identifying mother-child pairs within each homestead.

Since outcomes of interest from a child health point of view were utilization of routine services in infancy, such as for vaccination and growth monitoring, and the determination of growth and morbidity patterns during the first year of life, the age group of 12-23 months, for which these activities are likely to have been completed, was selected.

This provided the opportunity to concurrently determine utilization patterns for antenatal care, delivery, and family planning services for their mothers. The linkage of mothers to preschool children aged 12-23 months made it possible to:

• Establish retrospectively the health service utilization patterns and the health status of young children during the completed first year of life. This is the time when risks for morbidity and mortality are highest and attendance at clinic for preventive care is most critical.

• Access RTHCs most reliably and thereby provide objective evidence of clinic attendance, growth monitoring and vaccination coverage, conveniently perform anthropometrical assessment of the selected children.

Women in this category are also sufficiently close to the pregnancy to recall pregnancy- related events. It has also been shown in previous surveys (Damman

et al.,

1990;

Dammann & Solarsh, 1992; Wilkinson

et al.,

1997a) that the vast majority of mothers can produce RTHCs for children of this age and this therefore furnishes a source of objective health status and health service utilization data. The MI5 database did not contain pre-existing demographic data on households, although demographic data formed a basis for homestead selection. Since homesteads were initially sampled in the absence of any knowledge about age breakdown of its members, a number of the sampled homesteads did not have children of the required age.

In the absence of children aged 12-23 months, fieldworkers were required to move to the nearest adjacent homestead and to repeat this process until a homestead with a child of the required age was found. The preferred respondent in each case was the mother of the child if was still alive. If the mother was deceased the primary caregiver of the child was interviewed. If the motherjcaregiver was absent but was not a migrant (expected to return at sometime within a week of the first visit), fieldworkers were

required to revisit the homestead to conduct the interview with the mother/caregiver at a time when she was expected to be present. Other reasons for revisits were the absence of the index child or a RTHC at the time of the visit. If the child was unlikely to be available within one week of the first visit, another mother-child pair was selected from a nearby homestead. If the mother was unlikely to be available, the interview was conducted with the primary caregiver such as the granny, the stepmother or aunt. Only one mother-child pair was included from each selected homestead. If there were more than one child in the household, the names of the children were written on pieces of paper and put in a plastic bag and then selected one name randomly.