This 2011-12 Tanzania HIV/AIDS and Malaria Indicator Survey (THMIS) was implemented by the National Bureau of Statistics (NBS) in collaboration with the Office of the Chief Government Statistician (OCGS-Zanzibar) from December 16, 2011, to May 24, 2012.The Tanzania Commission for AIDS (TACAIDS) and the Zanzibar AIDS Commission authorized the National Bureau of Statistics (NBS) to conduct the 2011-12 THMIS. The survey covers both the Tanzania Mainland and Zanzibar.
The objectives of the 2011-12 THMIS were to collect data on knowledge and behaviour regarding HIV/AIDS and malaria, measure HIV prevalence among women and men age 15-49, and measure the presence of malaria parasites and anaemia among children age 6-59 months. The 2011-12 THMIS follows up on the 2007-08 THMIS and the 2003-04 Tanzania HIV/AIDS Indicator Survey (THIS). The 2011-12 THMIS also updates 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, the 2004-05 TDHS, and the 2010 TDHS.
Kind of data
Sample survey data [ssd]
- v01: Edited, anonymous datasets for public distribution.
Unit of analysis
The survey covered all de jure household members (usual residents), all eligible men and women aged between 15-49 years, and all children age 6-59 months in the household.
Producers and sponsors
National Bureau of Statistics
Tanzania Commission for AIDS
Zanzibar AIDS Commission
Support through MEASURE DHS project
Office of Chief Government Statistician-Zanzibar
United States Agency for International Development
Tanzania Commission for AIDS
Ministry of Health and Social Welfare
The sampling frame used for the 2011-12 THMIS was developed by the National Bureau of Statistics (NBS) after the 2002 Population and Housing Census (PHC) and is the same as that used for the 2010 and 2004-05 Tanzania Demographic and Health Surveys (TDHS), the 2007-2008 THMIS, and the 2003-04 Tanzania HIV and AIDS Indicator Survey (THIS). The sampling frame excluded nomadic and institutional populations such as persons in hotels, barracks, and prisons.
The 2011-12 THMIS was designed to allow estimates of key indicators for each of Tanzania's 30 regions. The sample was selected in two stages. The first stage involved selecting sample points (clusters) consisting of enumeration areas (EAs) delineated for the 2002 PHC. A total of 583 clusters were selected.On the Mainland, 30 sample points were selected in Dar es Salaam and 20 were selected in each of the other 24 regions.2 In Zanzibar, 15 sample points were selected in each of the five regions.
The second stage of selection involved the systemic sampling of households. 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. Approximately 18 households were selected from each sample point for a total sample size of 10,496 households.
The sampling procedures are more fully described in "Tanzania HIV/AIDS and Malaria Indicator Survey 2011-2012 - Final Report" pp.4-5.
A total of 10,496 households were selected for the sample, from both Mainland Tanzania and Zanzibar. Of these, 10,226 were found to be occupied at the time of the survey. A total of 10,040 households were successfully interviewed, yielding a response rate of 98 percent. In the interviewed households, 11,423 women were identified as eligible for the individual interview. Completed interviews were obtained for 10,967 women, yielding a response rate of 96 percent. Of the 9,388 eligible men identified, 8,352 were successfully interviewed (89 percent response rate).
The principal reason for nonresponse among both eligible women and men was the failure to find them at home despite repeated visits to the households. The lower response rate among men than among women was due to the more frequent and longer absences of men from the households.
Because of the approximately equal sample sizes in each region, the sample is not self-weighting 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.
Dates of collection
Mode of data collection
Data collection supervision
Main training participants also included 16 team supervisors from NBS and the Office of Chief Government Statistician-Zanzibar (OCGS) who were provided with additional training in methods of field editing, data quality control procedures, and fieldwork coordination.
Two questionnaires were used for the 2011-12 THMIS: the Household Questionnaire and the Individual Questionnaire. These questionnaires are based on the MEASURE DHS standard AIDS Indicator Survey and Malaria Indicator Survey questionnaires and were adapted to reflect the population and health issues relevant to Tanzania. Input was solicited from various stakeholders representing government ministries and agencies, nongovernmental organizations, development partners, and international donors. After the preparation of the definitive questionnaires in English, the questionnaires were translated into Kiswahili.
The Household Questionnaire was used to list all the usual members and visitors of selected households. Some basic demographic information was collected on the characteristics of each person, including his or her age, sex, education, and relationship to the head of the household. For children under age 18, survival status of the parents was determined. The data on age and sex of household members obtained in the Household Questionnaire was 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’s dwelling unit, such as the source of water, type of toilet facilities, materials used for the floor of the house, ownership of various durable goods, and ownership and use of mosquito nets. The Household Questionnaire was also used to record haemoglobin and malaria testing results for children age 6-59 months.
The Individual Questionnaire was used to collect information from all eligible women and men age 15-49. These respondents were asked questions on the following topics:
- Background characteristics (education, media exposure, etc.)
- Marriage and sexual activity
- Awareness and behaviour regarding HIV/AIDS and other sexually transmitted infections (STIs)
- Knowledge and awareness of malaria
- Other health issues
Female respondents were asked to provide their birth history for the six years preceding the interview and information about recent fever and treatment of fever for children born since January 2006.
All questionnaires for the THMIS were returned to the NBS central office in Dar es Salaam for data processing, which consisted of office editing, coding of open-ended questions, data entry, and editing computer-identified errors. The data were processed by a team of 10 data entry clerks, two data editors, one data entry supervisor, and one administrator of questionnaires; the latter checked that the clusters were completed according to the sample selection and that all members of the household eligible for individual interview were identified. One data editor had the additional responsibility of receiving the blood samples from the field and checking them before sending them to the appropriate laboratory. Data entry and editing were accomplished using CSPro software. The process of office editing and data processing was initiated mid-January 2012 and completed in late June 2012.
The estimates from a sample survey are affected by two types of errors: non-sampling errors and sampling errors. Non-sampling 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 2011-12 Tanzania HIV/AIDS and Malaria Indicator Survey (2011-12 THMIS) to minimize this type of error, non-sampling 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 2011-12 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 among all possible samples. Although the degree of variability is not known exactly, it can be estimated from the survey results.
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 2011-12 THMIS sample is the result of a multi-stage stratified design, and, consequently, it was necessary to use more complex formulas. Sampling errors are computed by SAS, using programs developed by ICF International. These programs use the Taylor linearization method of variance estimation for survey estimates that are means, proportions, or ratios. The Jackknife repeated replication method is used for variance estimation of more complex statistics such as fertility and mortality rates.
The estimates of sampling error are more fully described in appendix B in document "Tanzania HIV/AIDS and Malaria Indicator Survey 2011-2012 - Final Report" pp.199-200.
Other forms of data appraisal
A series of data quality tables are available to review the quality of the data and include the following:
- Age distribution of the household population
- Age distribution of eligible and interviewed women
- Age distribution of eligible and interviewed men
- Completeness of reporting
The results of each of these data quality tables are shown in appendix C in document "Tanzania HIV/AIDS and Malaria Indicator Survey 2011-2012 - Final Report" pp.227-229.
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.
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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:
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- 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 (AIS) 2011-2012. Ref. TZA_2011_AIS_v01_M. Dataset downloaded from http://www.measuredhs.com on [date]
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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.