National Income Dynamics Study 2008, Wave 1 Secure Data - South Africa

Abstract
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In 2008, the South African Presidency embarked on an intensive effort to track changes in the well-being of South Africans by closely following about 28 000 people - young and old, rich and poor - over a period of years. This was undertaken through initiating the National Income Dynamics Study (NIDS). The NIDS survey is the first national panel study to document the dynamic structure of a sample of household members in South Africa and changes in their incomes, expenditures, assets, access to services, education, health, and other dimensions of well-being. A key feature of the panel study is its ability to follow people as they move out of their original 7 305 households. In doing this, the movement of household members as they leave and/or return to the household or set up their own households will be adequately captured in subsequent waves of this panel study.

The first “baseline” wave of NIDS was conducted by the Southern Africa Labour and Development Research Unit (SALDRU) based at the University of Cape Town's School of Economics. The first wave of fieldwork commenced in February 2008, and data and report released in July 2009. The design of NIDS envisaged data collection every two years.

Elsewhere in the world such surveys have been invaluable in promoting understanding of who is making progress in a society and who is not and, importantly, what factors are driving these dynamics. In addition, panel data is invaluable for the purposes of evaluating and monitoring the efficacy of social policies and programmes. This is because the panel allows researchers and policy analysts to see how households and individuals are impacted when they become eligible for these programmes.

Geographic coverage
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The NIDS 2008 covered the whole of South Africa. The lowest level of geographic aggregation for the data is district municipality.

Analysis unit
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The units of analysis in the NIDS 2008 survey are individuals and households.

Universe
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The target population for NIDS 2008 was private households in all nine provinces of South Africa, and residents in workers' hostels, convents and monasteries. The frame excludes other collective living quarters, such as student hostels, old age homes, hospitals, prisons and military barracks.

Kind of data
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Sample survey data [ssd]

Sampling procedure
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A stratified, two-stage cluster sample design was employed in sampling the households to be included in the base wave. In the first stage, 400 Primary Sampling Units (PSUs) were selected from Stats SA's 2003 Master Sample of 3000 PSUs. This Master Sample was the sample used by Stats SA for its Labour Force Surveys and General Household Surveys between 2004 and 2007 and for the 2005/06 Income and Expenditure Survey. Each of these surveys was conducted on non-overlapping samples drawn within each PSU.

The sample of PSUs for NIDS is a subset of the Master Sample. The explicit strata in the Master Sample are the 53 district councils (DCs). The sample was proportionally allocated to the strata based on the Master Sample DC PSU allocation and 400 PSUs were randomly selected within strata. It should be noted that the sample was not designed to be representative at provincial level, implying that analysis of the results at province level is not recommended.

Sample of dwelling units

At the time that the Master Sample was compiled, 8 non-overlapping samples of dwelling units were systematically drawn within each PSU. Each of these samples is called a "cluster" by Stats SA. These clusters were then allocated to the various household surveys that were conducted by Stats SA between 2004 and 2007. However, two clusters in each PSU were never used by Stats SA and these were allocated to NIDS.

It was sometimes necessary to re-list a PSU when the situation on the ground had drastically changed to an extent that the information recorded on the listing books no longer reflected the situation on the ground. In these cases, the PSU was re-listed and a new sample of dwelling units selected. However, the downside of re-listing a PSU is that the chance of sample overlap with dwelling units that are in other surveys is increased. The extent of this overlap cannot be quantified as the lists are no longer comparable. There is anecdotal evidence that sample overlap might have occurred in some PSUs.

Individual respondent selection

Fieldworkers were instructed to interview all households living at the selected address/dwelling unit. If they found that the dwelling unit was vacant or the dwelling no longer existed they were not permitted to substitute the dwelling unit but recorded this information on the household control sheet.

The household control sheet is a two page form. This form was completed for every dwelling unit that was selected in the study, regardless of whether or not a successful interview was conducted. Where more than one household resided at the selected dwelling unit, a separate household control sheet was completed for every household and they were treated in the data as separate units. In order to qualify as separate households they should not share resources or food. Lodgers and live-in domestic workers were considered separate households.

All resident household members at selected dwelling units were included in the NIDS panel, providing that at least one person in the household agreed to participate in the study. The household roster in the household questionnaire was used to identify potential participants in the study. Firstly, respondents were asked to list all individuals that have lived under this "roof" or within the same compound/homestead at least 15 days during the last 12 months OR who arrived in the last 15 days and this was now their usual residence. In addition the persons listed should share food from a common 'pot' and share resources from a common resource pool. All those listed on the household roster are considered household members.

All resident household members became NIDS sample members. In addition, non-resident members that were "out of scope" at the time of the survey also became NIDS sample members. Out-of-scope household members were those living in insititutions (such as boarding school hostels, halls of residence, prisons or hospitals) which were not part of the sampling frame. These individuals had a zero probability of selection at their usual place of residence and were thus included in the NIDS sample as part of the household that had listed them as non-resident members. These two groups constitute the permanent sample members (PSMs) and should have had an individual questionnaire (adult, child or proxy) completed for them. These individuals are PSMs even if they refused to be interviewed in the base wave.

An initial sample of 9600 dwelling units was drawn with the expectation of realizing 8000 successful interviews. However, during the initial round of fieldwork for Wave 1 we did not achieve the target number of households. Therefore we went back to the field to attempt to overturn refusals in 48 PSUs and to visit 24 new dwelling units in 32 of these areas. Stats SA drew an additional 24 dwelling units from their Master Sample in predominantly White and Asian PSUs in order to improve representation of these population groups in the data.

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

Research instrument
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Four questionnaires were administered for the National Income Dynamics Study 2008:

HOUSEHOLD QUESTIONNAIRE: This covered household characteristics, household roster, mortality history, living standards, expenditure, consumption, negative events, positive events, agriculture
ADULT QUESTIONNAIRE: This was administered to all people in sampled households who were 15-years old or older on the day of the interview. The Adult Questionnaire collected data on demographics, education, labour market participation, income, health, well-being, numeracy and anthropometric measurements
CHILD QUESTIONNAIRE: This asked questions of household members who were 14-years old or younger, and covered education, health, family support, grants and numeracy and anthropometric data
PROXY QUESTIONNAIRE: These were completed where possible for adults who were unavailable or unable to answer their own adult questionnaire

Cleaning operations
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Initially the intention was that data capture would be done in-house. However, by early March 2008 it became evident that data capture was proceeding too slowly and Citizen Surveys was awarded the tender for the work.All questionnaires were double captured and anomolies reconciled. Regular data dumps enabled the checking of captured data against hard copies of the questionnaires.

Response rate
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Response rates in phase 1 of Wave 1 of the NIDS survey were disappointing and phase 2 was embarked upon to realise a more acceptable base wave sample. A detailed analysis of household level and individual level response rates follows. Item non-response rates are not addressed here. Such non-response is flagged in the data and is appropriately discussed in the context of specific analyses in the Discussion Paper series.

Household response rates were calculated using the number of visited dwelling units as the denominator and the number of participating households as the numerator. In the instances where response rates are given by race the predominant race group of the PSU is assigned to all households in that PSU. This is done because, by definition, non participating households were not interviewed and we did not gather information about the race of their members from the questionnaires.

Every effort was made to correctly identify all resident household members at the time of the interview. For different reasons not all resident household members were interviewed. For 1754 adults who were unavailable proxy questionnaires were completed. For a further 1250 adults no questionnaires were completed. For these individuals we only have the information supplied in the household roster, i.e. date of birth, education, etc. They are however panel members and we will attempt to make contact with them in the next wave.

Over the combined field work periods NIDS fieldworkers knocked on 10,642 household doors. Of these households, 7305 agreed to participate and the interview was completed. This equates to a 69% response rate. The total sample for NIDS consists of 409 PSUs. Of those, 9 were replaced in phase 2 because the whole PSU was inaccessible in phase 1. They are therefore excluded from the rest of the calculations.

摘要
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2008年，南非总统府启动了一项密集的努力，通过长期追踪约28,000名南非民众——包括年轻与老年、富有与贫困之人——的生活福祉变化，以追踪南非民众福祉的变化。这一举措通过启动国家收入动态研究（NIDS）而得以实施。NIDS调查是南非首个全国性面板研究，旨在记录样本家庭成员的动态结构及其收入、支出、资产、服务获取、教育、健康以及其他福祉维度的变化。面板研究的关键特征在于其追踪人们从原始7,305个家庭中移出的能力。在此过程中，家庭成员离开和/或返回家庭或建立自己的家庭时的流动情况将在面板研究的后续波次中得到充分记录。

NIDS的首个“基线”波次由位于开普敦大学经济学院的研究单位——南部非洲劳工与发展研究单元（SALDRU）实施。首波次实地调查于2008年2月开始，数据与报告于2009年7月发布。NIDS的设计预期每两年收集一次数据。

在世界其他地方，此类调查对于促进人们对在社会中谁在取得进步以及谁没有取得进步的理解，以及至关重要的，是什么因素驱动这些动态，具有无价的价值。此外，面板数据对于评估和监测社会政策和项目的有效性也极为宝贵。这是因为面板数据使研究人员和政策分析师能够看到，当家庭和个人有资格获得这些项目时，他们是如何受到影响的。

地理覆盖范围
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NIDS 2008涵盖了整个南非。数据的最小地理聚合级别为地区市镇。

分析单元
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NIDS 2008调查的分析单元为个人和家庭。

总体
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NIDS 2008的目标总体为南非所有九个省份的私人家庭，以及工人宿舍、女修道院和修道院居民。抽样框架不包括其他集体居住场所，如学生宿舍、养老院、医院、监狱和军事营房。

数据类型
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样本调查数据 [ssd]

抽样程序
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在抽样包括在基线波次中的家庭时，采用了分层、两阶段集群样本设计。在第一阶段，从Stats SA的2003年3,000个主要抽样单元（PSU）的主样本中选择了400个PSU。这个主样本是Stats SA在2004年至2007年之间用于其劳动力调查和一般家庭调查，以及2005/06收入和支出调查的样本。每个这些调查都是在每个PSU内部抽取的非重叠样本中进行的。

NIDS的PSU样本是主样本的一个子集。主样本中的明确层是53个地区议会（DC）。样本根据主样本DC PSU分配按比例分配到层中，并在层内随机选择了400个PSU。应注意的是，样本的设计不是为了在省级水平上具有代表性，这意味着不建议在省级水平上分析结果。

住宅单元样本

在主样本编制时，每个PSU内部系统地抽取了8个非重叠的住宅单元样本。这些样本由Stats SA称为“集群”。然后，这些集群被分配到Stats SA在2004年至2007年之间进行的各种家庭调查中。然而，每个PSU中的两个集群从未被Stats SA使用，这些集群被分配给了NIDS。

在某些情况下，当实地情况发生剧烈变化，以至于登记簿上记录的信息不再反映实地情况时，有时有必要重新列出PSU。在这些情况下，PSU被重新列出，并选择了新的住宅单元样本。然而，重新列出PSU的缺点是增加了与在其他调查中的住宅单元样本重叠的机会。这种重叠的程度无法量化，因为列表不再可比。有证据表明，在有些PSU中可能发生了样本重叠。

受访者选择

调查员被指示采访所有居住在选定地址/住宅单元的家庭。如果他们发现住宅单元空置或住宅不再存在，他们不允许用住宅单元进行替代，而是在家庭控制表上记录此信息。

家庭控制表是一种两页表格。该表格用于研究中的每个选定的住宅单元，无论是否进行了成功的采访。如果选定住宅单元中有多个家庭居住，则为每个家庭完成一份单独的家庭控制表，并在数据中将它们视为单独的单位。为了有资格被视为单独的家庭，它们不应共享资源或食物。寄宿者和住家佣工被视为单独的家庭。

选定住宅单元中的所有居民家庭成员都被纳入NIDS面板，前提是家庭中至少有一个人同意参与研究。家庭问卷中的家庭花名册用于识别研究的潜在参与者。首先，受访者被要求列出在过去12个月内至少在“屋顶”下或同一院落/住宅内居住了15天或以上，或在过去15天内到达并现在成为其常住地的人员。此外，列出的个人应从共同的‘锅’中分享食物，并从共同资源池中分享资源。所有列在家庭花名册上的人员都被视为家庭成员。

所有居住在选定住宅单元的家庭成员都成为NIDS样本成员。此外，当时“范围外”的非居住成员也成为NIDS样本成员。范围外的家庭成员是居住在机构（如寄宿学校宿舍、学生宿舍、监狱或医院）中的人，这些机构不是抽样框架的一部分。这些人通常居住地的选择概率为零，因此作为列出他们的家庭作为非居住成员的一部分被纳入NIDS样本。这两组构成了永久样本成员（PSM），为他们完成的应该是个人问卷（成人、儿童或代理）。即使他们在基线波次中拒绝接受采访，这些人也是PSM。

最初抽取了9,600个住宅单元样本，预计可实现8,000次成功的采访。然而，在第一波次实地调查的初始阶段，我们没有达到目标家庭数量。因此，我们回到实地，在48个PSU中尝试推翻拒绝，并在32个这些地区的24个新住宅单元中进行访问。Stats SA从其主样本中抽取了24个住宅单元，以改善这些地区的数据中白人和亚洲人口群体的代表性。

数据收集方式
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面对面 [f2f]

研究工具
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为2008年国家收入动态研究（NIDS）实施了四份问卷：

家庭问卷：涵盖家庭特征、家庭花名册、死亡史、生活水平、支出、消费、负面事件、正面事件、农业
成人问卷：对样本家庭中15岁或以上的人在采访当天进行实施。成人问卷收集了人口统计、教育、劳动力市场参与、收入、健康、福祉、算术和人体测量数据
儿童问卷：对14岁或以下的家庭成员进行提问，涵盖教育、健康、家庭支持、补助和算术以及人体测量数据
代理问卷：在可能的情况下，为无法或无法回答自己成人问卷的成人完成

清洗操作
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最初，计划在内部进行数据捕获。然而，到2008年3月初，很明显数据捕获进展得太慢，Citizen Surveys被授予该工作的投标。所有问卷都进行了双重捕获，并解决了异常情况。定期数据导出使人们能够将捕获的数据与问卷的硬拷贝进行核对。

响应率
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NIDS调查第一波次第一阶段的响应率令人失望，因此启动了第二阶段，以实现更可接受的基线波次样本。以下是对家庭层面和个人层面响应率的详细分析。此处不涉及项目非响应率。此类非响应在数据中被标记，并在讨论论文系列的具体分析中进行适当讨论。

家庭响应率是根据访问的住宅单元数量作为分母，参与的家庭数量作为分子来计算的。在响应率按种族给出的情况下，PSU的主要种族群体被分配给该PSU中的所有家庭。这是因为在定义上，未参与的家庭没有被采访，我们没有从问卷中收集有关其成员种族的信息。

尽一切努力在采访时正确识别所有居住家庭成员。由于不同的原因，并非所有居住家庭成员都被采访。对于1,754名无法采访的成年人，完成了代理问卷。对于另外1,250名成年人，没有完成问卷。对于这些人，我们只有家庭花名册中提供的信息，即出生日期、教育等。然而，他们是面板成员，我们将在下一波次尝试与他们取得联系。

在综合实地调查期间，NIDS调查员敲响了10,642个家庭的大门。在这些家庭中，7,305家同意参与，采访完成。这相当于69%的响应率。NIDS的总样本由409个PSU组成。其中，9个在第二阶段被替换，因为在第一阶段中整个PSU无法进入。因此，它们被排除在其他计算之外。