National Income Dynamics Study 2008, Wave 1 - 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.

Completed and non-response interviews in the NIDS Data:
The NIDS datasets contain both completed and non-response interviews (e.g. Refusals). It is recommended that researchers limit their research to completed interviews to avoid item non-response from non-response interviews. The completed interviews can be identified by making use of the w`x'_`y'_outcome variables, where `x' represents the wave and `y' represents the relevant data file/outcome type indicator. These outcome variables can be found in each of the following data files, Adult, Child, Proxy, HHQuestionnaire and Link File.
The only exception to this is Wave 1 where no outcome variable exists. This is because at a household level, all of the interviews are completed. However this does not apply at an individual level where non-response interviews can be identified by making use of the "Reason for refusal" variables, namely w1_a_refexpl or w1_c_refexpl in the Adult and Child data files respectively.

Geographic coverage
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The NIDS data is nationally representative. The survey began in 2008 with a nationally representative sample of over 28,000 individuals in 7,300 households across the country. The survey is repeated every two years with these same household members, who are called Continuing Sample Members (CSMs). The survey is designed to follow people who are CSMs, wherever they may be in SA at the time of interview. The NIDS data is therefore, by design, not representative provincially or at a lower level of geography (e.g. District Council).

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旨在通过长期追踪约28,000名——老幼、贫富——南非民众的生活福祉变化而进行的密集型工作。此项目通过启动国家收入动态研究（NIDS）得以实施。NIDS调查是南非首个记录样本家庭成员动态结构及其收入、支出、资产、服务获取、教育、健康及其他福祉维度的变化的国家面板研究。面板研究的关键特征在于其追踪人们在离开原7,305户家庭后的变化情况的能力。在此过程中，家庭成员离开、返回家庭或建立新家庭时的移动情况将在该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南非劳动与发展研究单位（SALDRU）实施。首次实地工作始于2008年2月，数据及报告于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，此类调查在促进对哪些社会成员取得进步以及哪些社会成员没有取得进步的理解方面具有无价的价值，并且，更重要的是，哪些因素推动了这些动态变化。此外，面板数据对于评估和监控社会政策和计划的有效性至关重要。这是因为面板数据允许研究人员和政策分析师观察家庭和个人在符合这些计划条件时受到的影响。

NIDS数据集中的完成和非响应访谈：
NIDS数据集包含完成和非响应访谈（例如，拒绝）。建议研究人员将研究范围限制在完成访谈，以避免来自非响应访谈的项目非响应。可以通过使用w`x'_`y'_outcome变量来识别完成访谈，其中`x'`代表波次，`y'`代表相关的数据文件/结果类型指标。这些结果变量可以在以下每个数据文件中找到，包括成人、儿童、代理人、家庭问卷和链接文件。
唯一例外的是波次1，其中不存在结果变量。这是因为从家庭层面来看，所有访谈都已完成。然而，这并不适用于个人层面，在个人层面，可以通过使用“拒绝原因”变量来识别非响应访谈，即成人数据文件中的w1_a_refexpl或儿童数据文件中的w1_c_refexpl。

地理覆盖范围
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NIDS数据在全国范围内具有代表性。调查始于2008年，对全国范围内7,300户家庭中的超过28,000名个人进行了抽样调查。调查每两年重复一次，调查同一户家庭成员，这些家庭成员被称为持续样本成员（CSMs）。调查旨在追踪在访谈时可能位于南非任何地方的CSMs。因此，NIDS数据按设计并非在省或更低地理级别（例如，区议会）具有代表性。

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的目标总体是南非所有九个省份的私营家庭，以及工人宿舍、修道院和修道院的居民。抽样框架不包括其他集体居住设施，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、两阶段集群抽样设计。在第一阶段，从Stats SA的2003年3,000个抽样单元（PSU）的主样本中选择了400个初级抽样单元（PSU）。此主样本是Stats SA在2004年至2007年期间用于其劳动力调查和一般家庭调查，以及2005/06年收入和支出调查的样本。每个这些调查都是在每个PSU内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个区议会（DC）。样本按主样本DC PSU分配的比例分配到层中，并在层内随机选择了400个PSU。应注意，样本并非设计为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
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