Malaria Indicator Survey 2011 - Angola

Abstract
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The 2011 Malaria Indicator Survey in Angola (2011 AMIS) was conducted by Cosep Consultoria, Consaúde Lda., and the Programa Nacional de Controle da Malária, with technical assistance from ICF Macro. Fieldwork took place from January 2011 through May 2011. The Angola Malara Indicator Survey (AMIS) is part of the Demographic and Health Surveys (MEASURE DHS) program and the Malaria Indicator Surveys (MIS) programs, implemented by ICF International under contract with USAID Washington. The objectives of the 2011 AMIS are (1) to evaluate behavior related to the prevention and treatment of malaria and (2) to estimate the prevalence of malaria among children under age 5. Additional questions were included to facilitate the estimation of fertility and infant mortality.

Fieldwork for the 2011 AMIS took place between January 2011 and May 2011, amidst heavy rains and floods typical of the period of high transmission of malaria. The survey collected data from 8,030 households and 8,589 women age 15-49. The sample was designed to represent populations at the national level, at urban and rural levels, and in four recognized malaria epidemiological regions: Hyperendemic, Mesoendemic Stable, Mesoendemic Unstable, and the Province of Luanda.

Geographic coverage
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National

Analysis unit
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- Household,
- Individual.

Universe
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The survey covered all de jure household members (usual residents), all women aged between 15-49 years, all children under age 5 living in the household.

Kind of data
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Sample survey data [ssd]

Sampling procedure
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OBJECTIVES OF THE SAMPLING DESIGN
(1) The 2011 AMIS survey was designed to determine reliable malaria prevalence estimates among children under age 5 at the various domains of interest (when feasible) and mortality estimates for children under age 5.
(2) The major domains to be distinguished in the tabulation of key indicators are:
- Angola at the national level
- The majority of indicators for each of the four domains defined for Angola and classified as the following regions:
1) Hyperendemic region, high malaria prevalence
2) Mesoendemic Stable region, medium malaria prevalence
3) Mesoendemic Unstable region, medium malaria prevalence, though prevalence is affected by the amount of rain
4) Luanda province
- Urban and rural areas of Angola (each as a separate domain)
- Any contiguous group of provinces with an adequate sample size of at least 1,500 households
(3) The primary objective of the 2011 AMIS is to provide estimates with acceptable precision for important population indicators associated with each domain, such as:
a. Ownership and use of mosquito bednets.
b. Practices to treat malaria among children under age 5 and the use of specific antimalarial drugs
c. Prevalence of malaria and anemia among children age 6-59 months
d. Knowledge, attitudes, and practices regarding malaria in the general population

SAMPLE FRAME
Administratively, Angola is divided into 18 provinces, which can be grouped into eight subregions depending on how they share some common factors.2 In turn, each province is subdivided into municipalities (164 in total), and each municipality is divided into communes (532 in total). Each commune is classified as either urban or rural. In addition to these administrative units, in preparation for the last population census, each urban commune was subdivided into segments named census sections (CSs) that were equivalent to enumeration areas. The National Statistical Institute (INE) had been preparing cartographic materials, including a count of rooms and dwellings, for each CS in the urban areas. This material became an appropriate sampling frame for the 2011 AMIS. However, INE does not have updated cartographic material for the rural areas. To compensate for this lack, INE uses its regional offices to collect a list of villages, with estimated populations in each village, for most of the rural communes,. To develop the sample frame for the 2011 AMIS, the list of CSs was used for the urban communes and the list of villages was used for the rural communes.

STRATIFICATION
The communes were grouped by major region, by rural or urban location, by sub-region, and by province as a way to identify homogeneous sampling units. In addition, within each urban commune, several CSs were grouped, taking advantage of the existing neighborhoods (sub-districts) for stratification of the sample.

SAMPLE SIZE
The following table includes different scenarios used to select a sample size in a populationbased survey. In the absence of domains, the numbers are valid for the entire population; however, if analyses are expected for more than one domain, then the numbers should be interpreted as required for each domain.

SAMPLE ALLOCATION
The clusters for the implementation of the 2011 AMIS are defined on the basis of census sections (CSs) for urban communes and on the basis of villages for rural communes. The 240 clusters considered for the 2011 AMIS were equally allocated at 60 clusters in each domain. The target for the 2011 AMIS was to select about 8,800 households. Therefore, the sample take is on average 36 selected households per cluster (i.e., 8,800/240). Clusters are distributed as 96 in the urban areas and 144 in the rural areas.

Under the final sample allocation, it is expected that each of the four major malaria regions in Angola will provide a minimum of about 2,200 completed women interviews, 2,100 children under age 5, and 2,000 births in the last five years. Neither the distribution of the 240 clusters among major regions nor the distribution of households in the sample is proportional to the estimated population distribution. This is due to the disproportional number of CSs among major regions. As a result, the sample for the 2011 AMIS is not a selfweighted household sample. Therefore, the 2011 AMIS sample is unbalanced for residence areas and regions and will require the design of a final weighting adjustment procedure to provide representative estimates for all the study domains.

SAMPLE SELECTION
The sample for the 2011 AMIS was selected using a stratified three-stage cluster design consisting of 240 clusters, with 96 in urban areas and 144 in rural areas. In each urban or rural area in a given region, clusters are selected systematically with probability proportional to size.

The sampling procedures are fully described in Appendix A of " Angola Malaria Indicator Survey 2011 - Final Report" pp.43-48.

Mode of data collection
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Face-to-face [f2f]

Research instrument
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Two types of questionnaires were used for the 2011 AMIS: a household questionnaire and another questionnaire for women age 15-49 in the households selected for the survey. The questionnaires were developed from the ones used for the 2006-07 malaria indicator survey, which followed the methodology of the Roll Back Malaria and MEASURE DHS programs.

The Household Questionnaire was used to list all the usual members and visitors who stayed in the selected households the night before the survey. It also identified women eligible for interviewing and children age 6-59 months eligible for anemia and malaria tests.

Basic information collected on the characteristics of each person included age, sex, and relationship to head of household. The Household Questionnaire was also used to collect information on characteristics of the household dwelling, such as the water source; type of toilet facilities; materials used for the roof, floors, and walls; possession of durable goods; and possession and use of mosquito nets.

The Woman’s Questionnaire, used to collect information for all women age 15-49, covered the following topics:
- Sociodemographic characteristics of the respondent
- Birth history
- Prenatal care and intermittent preventive treatment (IPT) of malaria during pregnancy for the most recent birth
- Treatment of malaria symptoms in children
- Malaria knowledge

The survey protocol was submitted to and approved by the National Ethical Review Committee of the National Malaria Control Program and by the Institutional Review Board (IRB) of ICF Macro.

Cleaning operations
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Data entry started two weeks after the beginning of fieldwork. Twelve data entry operators were used, six in the morning and six in the afternoon. They were supervised by the data processing manager, the questionnaire organizer, and the questionnaire editor. Control tables with data on interviewer and team performance were assessed periodically, especially during the first two weeks of fieldwork. The tables helped identify mistakes some teams made at the beginning of fieldwork; these mistakes resulted in extra supervisory field visits. Once the data entry was finalized, a consultant verified completeness of the questionnaires and consistency betwen data entry and the initial results.

Response rate
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A total of 8,806 households were selected, of which 8,493 were occupied. The total number of households interviewed was 8,030, yielding a household response rate of 95 percent.

A total of 8,746 eligible women were identified in these households, and interviews were completed for 8,589 women, yielding a response rate of 98 percent. Household response rates were 97 percent in urban areas and 93 percent in rural areas, and response rates for eligible women were 97 percent in urban areas and 99 percent in rural areas.

Sampling error estimates
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The sample of respondents selected in the 2011 AMIS is only one of many samples that could have been selected from the same population, using the same sample design and expected size. Each of these samples would yield results that differ somewhat from the results of the actual sample selected. The variability that would be observed between all possible samples constitutes the sampling error. Although the degree of variability is not known exactly, it can be estimated from the sample actually selected.

A sampling error is usually measured in terms of the standard error (SE). The standard error for a mean, percentage, difference, or any other statistic calculated from the data in the sample can be defined as the square root of the variance, which is a measure of the variation in all possible samples. For example, for any given statistic calculated from the sample, 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 households had been selected as a simple random sample, it would have been possible to use straightforward formulas for calculating sampling errors and the limits for the confidence intervals. However, as has been mentioned, the 2011 AMIS sample is the result of a complex, multi-stage stratified design, and, consequently, it was necessary to use more complex formulas that take the effects of stratification and clustering into consideration. It was possible to calculate the sampling errors for the 2011 AMIS using a computer program known as Module for Sampling Errors, included in the computer package ISSA (Integrated System for Survey Analysis). This program processes percentages or medians as a ratio estimate r = y/x where both the numerator y and the denominator x are random variables.

Sampling errors for the 2011 AMIS are calculated for selected variables considered to be of primary interest. The results are presented in this appendix for the country as a whole, for urban and rural areas, and for each endemic region. For each variable, the tables present the value of the statistic (R), its standard error (SE), the number of unweighted (N) and weighted (WN) cases, the design effect (DEFT), the relative standard error (SE/R), and the 95 percent confidence limits, i.e., the values R+2SE and R-2SE. The DEFT is considered undefined when the standard error for a simple random sample is zero (when the estimate is close to 0 or 1).

The confidence interval (for example, the one calculated for the variable “households with at least one ITN”) can be interpreted the following way: the overall proportion from the national sample is 0.345 and the standard error is 0.014. To obtain the 95 percent confidence limits, one adds and subtracts twice the standard error to the sample estimate, i.e., 0.345 ± 2 × 0.014. There is a high probability (95 percent) that the true average proportion of households with at least one ITN lies between 0.318 and 0.373.

For the total sample, the value of the design effect (DEFT), averaged over all variables, is 1.95. This means that, due to multi-stage clustering of the sample, the average standard error is increased by a factor of 1.95 over the value observed for a corresponding simple random sample. The actual precision differs from the precision expected during the design of the sample due to several factors: the final size of the sample versus the sample selected; the actual size of DEFT versus the expected; and the actual value of the estimate versus the expected estimate. In addition, the actual precision is different from the expected precision, separately, for each indicator.

The sampling errors are fully described in Appendix B of " Angola Malaria Indicator Survey 2011 - Final Report" pp.49-55.

Data appraisal
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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
- Completeness of reporting
- Births by calendar year
- Reporting of age at death in days
- Reporting of age at death in months

The results of each of these data quality tables are shown in Appendix C of "Angola Malaria Indicator Survey 2011 - Final Report" pp.57-60.

摘要
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2011年安哥拉疟疾指标调查（2011 AMIS）由Cosep咨询公司、Consاúde Lda.和全国疟疾控制计划执行，技术支持来自ICF Macro。实地调查于2011年1月至2011年5月进行。安哥拉疟疾指标调查（AMIS）是人口与健康调查（MEASURE DHS）项目和疟疾指标调查（MIS）项目的一部分，由ICF国际在USAID华盛顿的合同下实施。2011 AMIS的目标是（1）评估与疟疾预防和治疗相关的行为，以及（2）估计5岁以下儿童疟疾的患病率。还包括额外问题，以便利生育和婴儿死亡率的估计。
实地调查于2011年1月至5月进行，正值疟疾高传播期的强降雨和洪水期间。调查收集了8,030户家庭和8,589名15-49岁女性的数据。样本旨在代表国家层面、城乡层面以及四个公认的疟疾流行病学区域：高度流行区、中度流行稳定区、中度流行不稳定区和卢安达省的人口。
地理覆盖范围
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全国
分析单元
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- 家庭
- 个人。
总体
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调查覆盖了所有法定家庭成员（常住居民），所有15-49岁的女性，以及所有居住在家庭中的5岁以下儿童。
数据类型
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样本调查数据 [ssd]
抽样程序
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抽样设计的目标
（1）2011 AMIS调查旨在确定5岁以下儿童在不同兴趣领域的可靠疟疾患病率估计（当可行时）和5岁以下儿童的死亡率估计。
（2）在关键指标汇总中需要区分的主要领域包括：
- 安哥拉国家层面
- 安哥拉定义的四个领域中的每个领域的大多数指标，并按以下区域分类：
1）高度流行区，疟疾患病率高
2）中度流行稳定区，中等疟疾患病率
3）中度流行不稳定区，中等疟疾患病率，尽管患病率受降雨量影响
4）卢安达省
- 安哥拉的城市和农村地区（每个作为一个单独的领域）
- 任何有至少1,500户家庭足够样本量的连续省份组
（3）2011 AMIS的主要目标是提供对每个领域与每个领域相关的重要人口指标的估计，如：
a. 蚊帐的拥有和使用。
b. 治疗5岁以下儿童疟疾的实践和特定抗疟药物的使用
c. 6-59个月儿童疟疾和贫血的患病率
d. 关于疟疾的普遍人群的知识、态度和实践
样本框架
行政上，安哥拉分为18个省，根据共享的一些共同因素，可以将其分为8个次区域。转而，每个省被细分为市（共164个），每个市被细分为区（共532个）。每个区被分类为城市或农村。除了这些行政单位外，在最后一次人口普查的准备中，每个城市区被细分为称为普查区（CSs）的段，这些段相当于计数区域。国家统计局（INE）已为城市区的每个CS准备制图材料，包括房间和住宅的计数。这些材料成为2011 AMIS的适当抽样框架。然而，INE没有农村地区的最新制图材料。为了弥补这一不足，INE使用其地区办公室收集大多数农村区的村庄列表，以及每个村庄的估计人口。为了制定2011 AMIS的抽样框架，使用了CSs列表用于城市区，以及村庄列表用于农村区。
分层
区被按主要区域、农村或城市位置、次区域和省份分组，以识别同质抽样单元。此外，在每个城市区内部，几个CSs被分组，利用现有的邻里（次区域）进行样本分层。
样本量
以下表格包括用于基于人群调查选择样本量的不同场景。在没有领域的情况下，这些数字适用于整个人口；然而，如果预期要对多个领域进行分析，则应将这些数字解释为适用于每个领域的。
样本分配
2011 AMIS的实施集群基于城市区的普查区（CSs）和农村区的村庄。考虑的2011 AMIS的240个集群平均分配到每个领域60个集群。2011 AMIS的目标是选择约8,800户家庭。因此，样本抽取平均为每个集群36户（即，8,800/240）。集群分布为城市地区96个，农村地区144个。
在最终的样本分配中，预计安哥拉四个主要疟疾区域中的每个区域至少将提供约2,200份完成的女性访谈、2,100名5岁以下儿童和2,000名过去五年内的出生。240个集群在主要区域之间的分布以及样本中的家庭分布并不与估计的人口分布成比例。这是由于主要区域之间CSs的数量不成比例。因此，2011 AMIS的样本不是自加权家庭样本。因此，2011 AMIS的样本在居住区域和地区上不平衡，将需要设计最终的加权调整程序，以提供所有研究领域的代表性估计。
样本选择
2011 AMIS的样本使用分层三阶段集群设计选择，包括240个集群，其中城市地区96个，农村地区144个。在给定区域的每个城市或农村地区，集群以与规模成比例的概率系统地选择。
抽样程序在“安哥拉疟疾指标调查2011 - 最终报告”附录A的第43-48页中进行了全面描述。
数据收集方式
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面对面 [f2f]
研究工具
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2011 AMIS使用了两种类型的问卷：家庭问卷和用于调查中选家庭的15-49岁女性的问卷。这些问卷是从用于2006-07疟疾指标调查的问卷中开发的，该问卷遵循了“减少疟疾”和MEASURE DHS计划的方法。
家庭问卷用于列出调查前夜留在所选家庭的所有常住成员和访客。它还确定了有资格接受访谈的女性和6-59个月大的儿童，他们有资格接受贫血和疟疾测试。
收集的每个个人的基本特征信息包括年龄、性别和与户主的关系。家庭问卷还用于收集有关家庭住宅特征的信息，例如水源；卫生设施的类型；屋顶、地板和墙壁使用的材料；耐用商品的拥有情况；以及蚊帐的拥有和使用。
用于收集所有15-49岁女性信息的女性问卷涵盖了以下主题：
- 应答者的社会经济特征
- 出生史
- 最近一次出生的产前保健和疟疾间歇性预防治疗（IPT）
- 治疗儿童疟疾症状
- 疟疾知识
调查方案已提交并经国家疟疾控制计划的国家伦理审查委员会和ICF Macro的机构审查委员会（IRB）批准。
数据清理操作
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数据录入始于实地工作开始后的两周。使用了12名数据录入员，上午6名，下午6名。他们由数据处理经理、问卷组织者和问卷编辑监督。定期评估了控制表，其中包含关于访谈者和团队表现的数据，特别是在实地工作的前两周。这些表格有助于确定一些团队在实地工作初期犯下的错误；这些错误导致额外的监督现场访问。一旦数据录入完成，一名顾问验证了问卷的完整性和数据录入与初始结果之间的一致性。
响应率
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总共选择了8,806户家庭，其中8,493户有人居住。接受访谈的家庭总数为8,030户，家庭响应率为95%。
在这些家庭中确定了8,746名有资格的女性，完成了8,589名女性的访谈，响应率为98%。城市地区的家庭响应率为97%，农村地区的家庭响应率为93%，有资格的女性的响应率为97%（城市地区）和99%（农村地区）。
抽样误差估计
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2011 AMIS中选的受访者样本只是从同一人口中可以选出的许多样本之一，使用相同的样本设计和预期规模。每个这些样本都会产生与实际选定的样本结果略有不同的结果。所有可能样本之间观察到的可变性构成了抽样误差。尽管可变性的程度并不完全清楚，但它可以从实际选定的样本中估计。
抽样误差通常以标准误差（SE）来衡量。均值、百分比、差异或从样本中的数据计算出的任何其他统计量的标准误差可以定义为方差的平方根，方差是所有可能样本中变化程度的衡量标准。例如，对于从样本中计算出的任何给定统计量，该统计量的值将在该统计量的标准误差的加减两倍范围内落在95%的所有可能样本的相同大小和设计中。
如果家庭样本被选为简单随机样本，则可以使用简单的公式来计算抽样误差和置信区间的限制。然而，如前所述，2011 AMIS的样本是复杂的多阶段分层设计的结果，因此有必要使用更复杂的公式，这些公式考虑了分层和集群的影响。可以使用称为抽样误差模块的计算机程序计算2011 AMIS的抽样误差，该程序包含在计算机软件包ISSA（综合调查分析系统）中。该程序将百分比或中位数作为比率估计r = y/x处理，其中分子y和分母x都是随机变量。
为2011 AMIS中选定的被认为是主要兴趣变量的选定变量计算了抽样误差。结果按整个国家、城市和农村地区以及每个流行病学区域呈现。对于每个变量，表格显示了统计量的值（R）、其标准误差（SE）、未加权（N）和加权（WN）案例数、设计效应（DEFT）、相对标准误差（SE/R）和95%置信区间，即R+2SE和R-2SE的值。当简单随机样本的标准误差为零时（当估计值接近0或1时），DEFT被认为是未定义的。
置信区间（例如，为“至少有一张ITN的家庭”变量计算的置信区间）可以按以下方式解释：国家样本的整体比例为0.345，标准误差为0.014。要获得95%置信区间，将两次标准误差加到样本估计值上，即0.345 ± 2 × 0.014。有很高的可能性（95%）表明，具有至少一张ITN的家庭的真实平均比例介于0.318和0.373之间。
对于整个样本，所有变量的设计效应（DEFT）的平均值是1.95。这意味着由于样本的多阶段集群，平均标准误差比相应的简单随机样本观察到的值增加了1.95倍。实际精度与设计样本期间预期的精度不同，这归因于几个因素：样本的最终大小与所选样本的大小；实际DEFT与预期的大小；以及估计值与预期估计值。
抽样误差在“安哥拉疟疾指标调查2011 - 最终报告”附录B的第49-55页中进行了全面描述。
数据评估
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有一系列数据质量表格可用于审查数据质量，包括以下内容：
- 家庭人口年龄分布
- 有资格和接受访谈的女性的年龄分布
- 报告的完整性
- 日历年度出生
- 死亡年龄以天为单位报告
- 死亡年龄以月为单位报告

这些数据质量表格的结果在“安哥拉疟疾指标调查2011 - 最终报告”附录C的第57-60页中展示。