The 2007-08 Tanzania HIV/AIDS and Malaria Indicator Survey (THMIS) is the second population-based, comprehensive survey on HIV/AIDS carried out in Tanzania.
The primary objectives of the 2007-08 THMIS survey were to provide up-to-date information on the prevalence of HIV infection among Tanzanian adults, and the prevalence of malaria infection and anaemia among children under age five years. The findings will be used to evaluate ongoing programmes and to develop new health strategies. Where appropriate, the findings from the 2007-08 THMIS are compared with those from the 2003-04 Tanzania HIV/AIDS Indicator Survey (THIS). The findings of these two surveys are expected to complement the sentinel surveillance system undertaken by the Ministry of Health and Social Welfare under its National AIDS Control Programme (NACP). The THMIS also provides updated estimates of selected basic demographic and health indicators covered in previous surveys, including the 1991-92 Tanzania Demographic and Health Survey (TDHS), the 1996 TDHS, the 1999 Reproductive and Child Health Survey (RCHS), and the 2004-05 TDHS.
More specifically, the objectives of the 2007-08 THMIS were:
- To measure HIV prevalence among women and men age 15-49;
- To assess levels and trends in knowledge about HIV/AIDS, attitudes towards people infected with the disease, and patterns of sexual behaviour;
- To collect information on the proportion of adults who are chronically sick, the extent of orphanhood, levels of and care and support;
- To gauge the extent to which these indicators vary by characteristics such as age, sex, region, education, marital status, and poverty status; and
- To measure the presence of malaria parasites and anaemia among children age 6-59 months.
The results of the 2007-08 THMIS are intended to provide information to assist policymakers and programme implementers to monitor and evaluate existing programmes and to design new strategies for combating the HIV/AIDS epidemic in Tanzania. The survey data will also be used as inputs in population projections and to calculate indicators developed by the United Nations General Assembly Special Session (UNGASS), the UNAIDS Programme, and the World Health Organization (WHO).
Kind of Data
Sample survey data [ssd]
Unit of Analysis
- Women age 15-49
- Men age 15-49
- Anemia Testing
- GPS/Georeferenced–Global Positioning System or Georeferenced Data
- HIV Behavior
- HIV Knowledge–Questions assess knowledge/sources of knowledge/ways to avoid HIV
- HIV Testing
- Malaria Module (bednets)
- Malaria parasitemia test
- Men's Survey
- TB Questions
Producers and sponsors
National Bureau of Statistics (NBS)
Macro International Inc
Technical assistance through MEASURE DHS
Tanzania Commission for AIDS
Zanzibar AIDS Commission
Office of Chief Government Statistician
United States Agency for International Development
SAMPLE SIZE AND DESIGN
The sampling frame used for the 2007-08 THMIS is the same as that used for the 2004-05 TDHS, which was developed by NBS after the 2002 Population and Housing Census (PHC). The sample excluded nomadic and institutional populations, such as persons staying in hotels, barracks, and prisons. The THMIS utilised a two-stage sample design. The first stage involved selecting sample points (clusters) consisting of enumeration areas delineated for the 2002 PHC. A total of 475 clusters were selected. The sample was designed to allow estimates of key indicators for each of Tanzania's 26 regions. On the Mainland, 25 sample points were selected in Dar es Salaam and 18 in each of the other 20 regions. In Zanzibar, 18 sample points were selected in each of the five regions, for a total of 90 sample points.
A household listing operation was undertaken in all the selected areas prior to the fieldwork. From these lists, households to be included in the survey were selected. The second stage of selection involved the systematic sampling of households from these lists. Approximately 16 households were selected from each sampling point in Dar es Salaam, and 18 households per sampling point were selected in other regions. In Zanzibar, approximately 18 households were selected from each sampling point in Unguja, and 36 households were selected in Pemba to allow reliable estimates of HIV prevalence for each island group.
Because of the approximately equal sample sizes in each region, the sample is not selfweighting at the national level, and weighting factors have been added to the data file so that the results will be proportional at the national level.
In the selected households, interviews were conducted with all women and men age 15-49. The THMIS also collected blood samples for anaemia and malaria testing among children age 6
A total of 9,144 households were selected for the sample, from both Mainland Tanzania and Zanzibar. Of these, 8,704 were found to be occupied at the time of the survey. A total of 8,497 households were successfully interviewed, yielding a response rate of 98 percent. In the interviewed households, 9,735 women were identified as eligible for the individual interview. Completed interviews were obtained for 9,343 women, yielding a response rate of 96 percent. Of the 7,935 eligible men identified, 6,975 were successfully interviewed (88 percent response rate). The differential is likely due to the more frequent and longer absence of men from the households. The response rates for urban and rural areas do not vary much.
Note: See summarized responses rate by urban/rural in Table 1.1 which is provided in this documentation.
Dates of Data Collection
Data Collection Mode
Data Collection Notes
TRAINING OF FIELD STAFF
Field staff training was conducted in Morogoro from 24 September to 12 October 2007. The training was conducted according to the AIS/MIS training procedures, including class presentations, mock interviews, field practice and tests. Participants included 14 team supervisors from NBS, OCGS-Zanzibar, former Ministry of Planning and Economic Empowerment, and the Ministry of Health and Social Welfare. In total, 59 female nurses, 23 male nurses, and 2 office data editors were trained to carry out the survey. Trainers were senior staff from NBS, OCGS-Zanzibar, and NMCP, as well as a laboratory technician from Muhimbili University College of Health Sciences (MUCHS).
Field practice in malaria and anaemia testing and HIV dried blood spot collection were carried out towards the end of the training period. During this period, field editors and team supervisors were provided with additional training in methods of field editing, data quality control procedures, and fieldwork coordination.
Data collection was carried out by 14 field teams, each consisting of one team leader, four female interviewers, one male interviewer, and one driver. Five senior staff members from NBS and OCGS-Zanzibar coordinated and supervised the fieldwork activities. Fieldwork on the Mainland started on 20 October 2007. Delay in obtaining ethical clearance for the Zanzibar fieldwork resulted in a delay in starting data collection in Zanzibar until 10 November 2007. Data collection took place over a four-month period, from 20 October 2007 to 22 February 2008.
A quality control team periodically visited teams in the field to check their work and reinterview some households.
National Bureau of Statistics
Two questionnaires were used for the 2007-08 THMIS: the Household Questionnaire and the Individual Questionnaire. The questionnaires are based on the standard AIDS Indicator Survey and Malaria Indicator Survey questionnaires, adapted for the population and health issues relevant to Tanzania. Inputs were solicited from various stakeholders representing government ministries and agencies, nongovernmental organizations, and international partners. After the preparation of the definitive questionnaires in English, questionnaires were translated into Kiswahili.
The Household Questionnaire was used to list all the usual members and visitors of selected households. Some basic information was collected on the characteristics of each person listed, including his or her age, sex, education, and relationship to the head of the household. For children under age 18 years, survival status of the parents was determined. If a child in the household had a parent who was sick for more than three consecutive months in the 12 months preceding the survey or a parent who had died, additional questions related to support for orphans and vulnerable children were asked. The Household Questionnaire also included questions on whether household members were seriously ill and whether anyone in the household had died in the past 12 months. In such cases, interviewers asked whether the household had received various kinds of care and support, such as financial assistance, medical support, social or spiritual support.
The Household Questionnaire was also used to identify women and men who were eligible for the individual interview and HIV testing. The Household Questionnaire also collected information on characteristics of the household dwelling, such as source of water, type of toilet facilities, materials used to construct the house, ownership of various durable goods, and ownership and use of mosquito nets.
Furthermore, the Household Questionnaire was used to record haemoglobin and malaria testing results for children age 6-59 months.
The Individual Questionnaire was used to collect information from all women and men age 15-49. These respondents were asked questions on the following topics:
• Background characteristics (education, residential history, media exposure, employment, etc.);
• Marriage and sexual activity;
• Knowledge about HIV/AIDS and exposure to specific HIV-related mass media programmes;
• Attitudes towards people living with HIV/AIDS;
• Knowledge and experience with HIV testing;
• Knowledge and symptoms of other sexually transmitted infections (STIs); and
• Other health issues including knowledge of TB and medical injections.
Female respondents were asked about their birth history and illnesses of children they gave birth to since January 2002. These questions are used to gauge the prevalence of fever, an important symptom of malaria.
All questionnaires collected during the THMIS fieldwork were periodically brought from the field to the NBS headquarters in Dar es Salaam for processing, which consisted of office editing, coding of open-ended questions, data entry, and editing of computer-identified errors. The data were processed by a team of 9 data entry clerks, 2 data editors, and 2 data entry supervisors. An administrator was assigned to receive and check the blood samples coming from the field. Data entry and editing were accomplished using the CSPro software. All data were entered twice (100 percent verification). The concurrent processing of the data was a distinct advantage for data quality because THMIS staff were able to advise the field teams of errors detected during data entry. The process of office editing and data processing was initiated on 8 November 2007 and completed on 7 April 2008. Dried blood spot (DBS) samples received from the field were logged in at NBS, checked, and transported to MUCHS for testing. The processing of DBS samples for HIV testing at MUCHS was handled by six laboratory scientists. The DBS samples were logged into the CSPro HIV Test Tracking System database, each given a laboratory number, and stored at -20°C until tested.
Estimates of Sampling Error
The estimates from a sample survey are affected by two types of errors: (1) nonsampling errors, and (2) sampling errors. Nonsampling errors are the results of mistakes made in implementing data collection and data processing, such as failure to locate and interview the correct household, misunderstanding of the questions on the part of either the interviewer or the respondent, and data entry errors. Although numerous efforts were made during the implementation of the 2007-08 Tanzania HIV/AIDS and Malaria Survey (THMIS) to minimize this type of error, nonsampling errors are impossible to avoid and difficult to evaluate statistically.
Sampling errors, on the other hand, can be evaluated statistically. The sample of respondents selected in the 2007-08 THMIS is only one of many samples that could have been selected from the same population, using the same design and expected size. Each of these samples would yield results that differ somewhat from the results of the actual sample selected. Sampling errors are a measure of the variability between all possible samples. Although the degree of variability is not known exactly, it can be estimated from the survey results.
A sampling error is usually measured in terms of the standard error for a particular statistic (mean, percentage, etc.), which is the square root of the variance. The standard error can be used to calculate confidence intervals within which the true value for the population can reasonably be assumed to fall. For example, for any given statistic calculated from a sample survey, the value of that statistic will fall within a range of plus or minus two times the standard error of that statistic in 95 percent of all possible samples of identical size and design.
If the sample of respondents had been selected as a simple random sample, it would have been possible to use straightforward formulas for calculating sampling errors. However, the 2007-08 THMIS sample is the result of a multi-stage stratified design, and, consequently, it was necessary to use more complex formulae. The computer software used to calculate sampling errors for the 2007-08 THMIS is the ISSA Sampling Error Module. This module used the Taylor linearization method of variance estimation for survey estimates that are means or proportions. The Jackknife repeated replication method is used for variance estimation of more complex statistics such as fertility and mortality rates.
Note: See detailed sampling error calculation in the APPENDIX B of the final report which is presented in this documentation.
Data and Data Related Resources
MEASURE DHS believes that widespread access to survey data by responsible researchers has enormous advantages for the countries concerned and the international community in general. Therefore, MEASURE DHS policy is to release survey data to researchers after the main survey report is published, generally within 12 months after the end of fieldwork. with few limitations these data have been made available for wide use.
DISTRIBUTION OF DATASETS
MEASURE DHS is authorized to distribute, at no cost, unrestricted survey data files for legitimate academic research, with the condition that we receive a description of any research project that will be using the data.
Registration is required for access to data.
Datasets are available for download to all registered users, free of charge. To download datasets, you must first register online and request the country(ies) and datasets that you are interested in. When submitting a dataset request, users must include a brief description of how the data will be used.
Datasets are made available with the following conditions:
- Survey data files are distributed by MEASURE DHS for academic research/statistical analysis. Researchers need to provide a description of any research/analysis that will be using the data, before access is granted to the datasets.
- Once downloaded, the datasets must not be passed on to other researchers without the written consent of MEASURE DHS.
- All reports and publications based on the requested data must be sent to the MEASURE DHS Data Archive as a Portable Format Document (pdf) or a hard copy, for us to forward to the country(ies) whose data have been used.
Use of the dataset must be acknowledged using a citation which would include:
- the Identification of the Primary Investigator
- the title of the survey (including country, acronym and year of implementation)
- the survey reference number
- the source and date of download
National Bureau of Statistics. Tanzania HIV/AIDS and Malaria Indicator Survey 2007-2008. Dataset downloaded from http://www.measuredhs.com on [date]
Disclaimer and copyrights
The user of the data acknowledges that the original collector of the data, the authorized distributor of the data, and the relevant funding agency bear no responsibility for use of the data or for interpretations or inferences based upon such uses.