Kagera Health and Development Survey 2010, Wave 6

KHDS 1991-1994 Household Sample: First Stage

The KHDS 91-94 household sample was drawn in two stages, with stratification based on geography in the first stage and mortality risk in both stages. A more detailed overview of the sampling procedures is outlined in "User's Guide to the Kagera Health and Development Survey Datasets." (World Bank, 2004).

In the first stage of selecting the sample, the 550 primary sampling units (PSUs) in Kagera region were classified according to eight strata defined over four agronomic zones and, within each zone, the level of adult mortality (high and low). A PSU is a geographical area delineated by the 1988 Tanzanian Census that usually corresponds to a community or, in the case of a town, to a neighbourhood. Enumeration areas of households were drawn randomly from the PSUs in each stratum, with a probability of selection proportional to the size of the PSU.

Within each agronomic zone, PSUs were classified according to the level of adult mortality. The 1988 Tanzanian Census asked a 15 percent sample of households about recent adult deaths. Those answers were aggregated at the level of the "ward", which is an administrative area that is smaller than a district. The adult mortality rate (ages 15-50) was calculated for each ward and each PSU was assigned the mortality rate of its ward.

Because the adult mortality rates were much higher in some zones than others and the distribution was quite different within zones, "high" and "low" mortality PSUs were defined relative to other PSUs within the same zone. A PSU was allocated to the "high" mortality category if its ward adult mortality rate was at the 90th percentile or higher of the ward adult mortality rates within a given agronomic zone.

The KHDS 91-94 selected 51 communities as primary sampling units (also referred to as enumeration areas or clusters). In actuality, two pairs of enumeration areas were within the same community (in the sense of collecting community data on infrastructure, prices or schools). Thus, for community-level surveys, there are 49 areas to interview.

KHDS 1991-1994 Household Sample: Second Stage

The household selection at the second stage (with enumeration areas) was a stratified random sample, where households which were expected to experience an adult death were oversampled. In order to stratify the population, an enumeration of all households was undertaken.

Between March 15 and June 13, 1991, 29,602 households were enumerated in the 51 areas. In addition to recording the name of the head of each household, the number of adults in the household (15 and older), and the number of children, the enumeration form asked:

1. Are any adults in this household ill at this moment and unable to work? If so, the age of the sick adult and the number of weeks he/she has been too sick to work were also noted.
2. Has any adult 15-50 in this household died in the past 12 months? If so, the age of each adult and the cause of death (illness, accident, childbirth, other) were also noted.

The enumeration form asked explicitly about illness and death of adults between the ages of 15-50 because this is the age group disproportionately affected by the HIV/AIDS epidemic; it is the impact of these deaths that was of research interest. Out of over 29,000 households enumerated, only 3.7 percent, or 1,101, had experienced the death of an adult aged 15-50 caused by illness during the 12 months before the interview and only 3.9 percent, or 1,145, contained a prime-age adult too sick to work at the time of the interview. Only 77 households had both an adult death due to illness and a sick adult. This supports the point that, even with some stratification based on community mortality rates and in an area with very high adult mortality caused by an AIDS epidemic, a very large sample would have had to have been selected to ensure a sufficient number of households that would experience an adult death during the two-year survey.

Using data from the enumeration survey, households were stratified according to the extent of adult illness and mortality. It was assumed that in communities suffering from an HIV epidemic, a history of prior adult death or illness in a household might predict future adult deaths in the same household. The households in each enumeration area were classified into two groups, based on their response to the enumeration:

1. Sick" households: Those that had either an adult death (aged 15-50) due to illness in the past 12 months, an adult too sick to work at the time of the survey, or both (n=2,169).
2. "Well" households: Those that had neither an adult death (aged 15-50) due to illness nor an adult (aged 15-50) too sick to work (n=27,433).

In selecting the sixteen households to be interviewed in each enumeration area, fourteen were selected at random from the "sick" households in that enumeration area and two were selected at random from the "well" households. In one enumeration area, where the number of "sick" households available was less than fourteen, all available sick households were included in the sample; the numbers were balanced using well households. The final sample drawn for the first passage consisted of 816 households in 51 enumeration areas.

KHDS 2004 and 2010 Household Samples

The sampling strategy in KHDS 2004 and KHDS 2010 was to re-interview all individuals who were household members in any wave of the KHDS 91-94, a total of 6,353 people. The Household Questionnaire was administered in the household in which these PHHMs lived. If a household member was alive during the last interview in 1991-1994, but found to be deceased by the time of the fieldwork in 2004 and 2010 then the information about the deceased was collected in the Mortality Questionnaire. The next sections provide statistics of the KHDS 2004 and 2010 households.

KHDS 2004 Households

Although the KHDS is a panel of individuals and the concept of a household after 10-19 years is a vague notion, it is common in panel surveys to consider re-contact rates in terms of households. Table 4 shows the rate of re-contact of the baseline households in KHDS 2004, where a re-contact is defined as having interviewed at least one person from the household. In this case, the term household is defined by the baseline KHDS survey which spans a period of 2.5 years. Due to movements in and out of the household, some household members may have not, in fact, lived together in the household at the same time in the 1991-1994 waves (for example, consider one sibling of the household head moving into the household for one year and then moving out, followed by another sibling moving into the household).

Excluding households in which all previous members are deceased (17 households and 27 respondents), the KHDS 2004 field team managed to re-contact 93 percent of the baseline households. Not all 915 households received four interviews. Unsurprisingly, households that were in the baseline survey for all four waves had the highest probability of being reinterviewed. Of these 746 households, 96 percent were re-interviewed.

Turning to re-contact rates of the sample of 6,353 respondents, Table 5 shows the status of the respondents by age group (based on their age at first interview in the 1991-1994 waves). Reinterview rates are monotonically decreasing with age, although the reasons (deceased or not located) vary by age group. The older respondents were much more likely to be located if alive. Among the youngest respondents, over three-quarter were successfully re-interviewed. Excluding people who died, 82 percent of all respondents were re-interviewed.

KHDS 2010 Households

The re-contact rates in the KHDS 2010 are in line with the ones achieved in KHDS 2004. Table 4 of the Basic Information Document shows the KHDS 2010 re-contacting rates in terms of the baseline households. Excluding the households in which all PHHMs were deceased, 92 percent of the households were recontacted.

As in KHDS 2004, households that were interviewed four times at the baseline were more likely to be found in 2010. Excluding the households in which all members had died, 95 percent of these households were re-interviewed in 2010.

The KHDS 2010 re-contact rates in terms of panel respondents are provided in Table 5 of the Basic Information Document. As in 2004, the older respondents, if alive, were much more likely to be re-contacted than younger respondents. In the oldest age category, 60 years and older at the baseline, the interview teams managed to re-contact almost 98 percent of all survivors. The length of the KHDS survey starts to be seen in this age category however, as almost three quarters of the respondents had passed away by 2010.

Table 6 of the Basic Information Document provides the KHDS 2010 re-contact rates by location. More than 50 percent of the reinterviewed panel respondents were located in the same community as in KHDS 91-94. Nearly 14 percent of the re-contacted respondents were found from other region than Kagera. The survey team also tracked panel respondents in Uganda where one percent of the interviewed panel respondents were located.

The location of the untraced respondents is based on the tracking data. More than half of the untraced respondents are reported to be living in Kagera.