Demographic and Health Survey 1987 - Sri Lanka

Abstract
---------------------------

The Demographic and Health Survey (DHS) is an important link in a chain of surveys carried out in Sri Lanka in the past decade or so. Having been designed as part of an international survey program and modelled on the lines of the well renowned World Fertility Survey (WFS) program, the DHS provides an exceptionally valuable source of data for the estimation of trends over time within Sri Lanka as well as for cross national comparison.

The survey focussed primarily on fertility, contraception and child mortality as did WFS but. also measured several indicators of child health, particularly immunization coverage and nutrition status. The inclusion of health sector information has been welcome and fruitful, for improve- ment of nutrition status is a subject to which the Government of Sri Lanka has accorded high priority.

The Sri Lanka Demographic and Health Survey has the following objectives:
1. To provide policymakers and administrators with current and accurate data on fertility, morbidity, family planning and selected indicators of health status which could be used for planning new strategies for the wellbeing of the population; etc.
2. To provide data which can be used to analyze trends over time. The SLDHS examines many of the same fertility, mortality, and health issues that were addressed in earlier surveys, most notably the SLWFS and the more recent SLCPS; and
3. To add to the international body of data which can be used for comparative studies.

Geographic coverage
---------------------------

National

Analysis unit
---------------------------

- Household
- Women age 15-49

Universe
---------------------------

In principle, the sample was designed to cover private households in the areas sampled. The population residing in institutions and institutional households was excluded. For the detailed individual interview, the eligibility criteria were: ever-married women aged 15 through 49 who slept in the household the previous night.

Kind of data
---------------------------

Sample survey data

Sampling procedure
---------------------------

SURVEY SAMPLE DESIGN

On the basis of socio-economic and ecological criteria, and the experience of the SLWFS, nine zones were created. It was felt that some of the six SLWFS zones were too heterogeneous and should be redrawn as shown in Figure i.i and described below:

Zone 1 - Colombo Metropolitan area consisting of SLWFS zone 1 and parts of zone 2.
Zone 2 - Colombo feeder areas and Northern part of SLWFS zone 2.
Zone 3 - South Western coastal low lands corresponding to Southern part of SLWFS zone 2.
Zone 4 - Lower South Central hill country corresponding to Western and Southern part of SLWFS zone 6, excluding districts with a concentration of estates.
Zone 5 - South Central hill country corresponding to part of SLWFS zone 5 with a concentration of estates.
Zone 6 - Irrigated Dry Zone corresponding to SLWFS zone 3, with major or minor irrigation schemes.
Zone 7 - Rain fed Dry Zone covering the rest of SLWFS zone 3.
Zone 8 - Eastern Coastal Belt, corresponding to SLWFS zone 4 (not included in SLDNS).
Zone 9 - Northern Province corresponding to SLWFS zone 5 (not included in SLDHS).

The changes SLDHS made to the SLWFS zones were designed: a) to separate the Colombo urban feeder areas from rural hinterlands; b) to separate rural areas with predominantly estate populations from other rural areas; and c) to distinguish between irrigated dry zone areas which are new settlements under development projects from those areas which rely primarily on rains for cultivation.

Although the survey originally planned to conduct interviews in all nine zones, Civil disturbances in zones 9 and 8 (the Northern and Eastern provinces) prevented interviews from being conducted there. These zones, which contain approximately 14 percent of the 1986 estimated population of Sri Lanka, have been excluded from the SLDHS.

With the exception of zone 5, the sample was allocated equally between zones with an estimated target 900 completed individual interviews per zone. Zone 5 was given a larger target sample size of 1,350 to permit over sampling of the estate plantation workers.

In principle, the sample was designed to cover private households in the areas sampled. The population residing in institutions and institutional households was excluded. For the detailed individual interview, the eligibility criteria were: ever-married women aged 15 through 49 who slept in the household the previous night.

For the selection of area units, the sample frame was based on block statistics from the 1981 Census of Population and Housing. However, these figures were updated where possible on the basis of the work done in connection with a 1985-86 labour force survey. This applied in particular to newly settled areas with the development of irrigation schemes in the dry zone. For the final selection of housing units within ultimate area units, a special operation was undertaken before the survey to update household lists within selected census blocks.

The zones created by the SLDHS, which were designed to capture relatively homogeneous subgroups of the population, served as the primary strata. Each zone was further stratified into (up to) three strata: urban, rural, and estate areas. Further implicit stratification was achieved by ordering the sampling areas according to administrative and geographical location. Similar systematic sampling procedures were followed at all stages up to and including the selection of housing units.

The sampling of housing units was undertaken in two or three stages depending upon the stratum. In densely populated zones i, 2, and 3, and in urban strata of all zones a three stage design was used:

At the first stage, a stratified sample of Gram Savaka or equivalent areas (waras or estates) with probability proportional to size (PPS) was selected. The number of primary sampling units (PSIs) selected was 54 in zones 5 and 36 in each of the other zones. Within a given zone, the number to be selected in a stratum was allocated proportionately to the strata populations.

1.Within each PSU, two census blocks were selected with PPS, systematically without replacement.
2.The final stage consisted of the selection of the housing units in selected blocks with inverse PPS so as to yield a self weighting sample within each stratum.

For the main survey, there was no further sampling as all eligible women in each selected housing unit were taken into the sample. Also, for the anthropometric measurements, all children 3 through 36 months of eligible women were taken.

In the non-urban strata in zones 3 through 7, the only difference in procedures was that generally only one block was selected per PSU. This procedure effectively reduced the number of stages to two: blocks as the first stage and housing units as the second stage.

Since zones were allocated generally uniform sample sizes, the overall sampling fractions varied in inverse proportion to the zone population.

Sampling deviation
---------------------------

It is important to note once again that the districts in the northern and eastern portions of the country were not covered by the SLDHS because of civil disturbances. Whenever comparisons are made between the SLDHS and the earlier SLWFS and SLCPS, the differences in areas covered by the surveys should be kept in mind.

Mode of data collection
---------------------------

Face-to-face

Research instrument
---------------------------

The Sri Lanka Demographic and Health Survey used two questionnaires each of which was pretested.

a) The first, called the Household Questionnaire, was used to list all usual household members and any visitors who slept in the household the preceding night. For each person listed, information on age, sex, and marital status and whether or not he/she slept in the household the previous night was recorded. From this list eligible respondents were selected for interview. An eligible respondent is defined as a woman currently married, divorced, separated, or widowed between the ages of 15 and 49 who slept in the household the previous night.

b) The second or Individual Questionnaire was administered to each eligible respondent. On the average, an individual interview took approximately 35 to 40 minutes. The Individual Questionnaire consisted of nine sections:
1. Respondents background
2. Birth history-dates of all live births and infant and child deaths
3. Contraception-knowledge, ever use, current use and a detailed history of inter birth use in the last 5 years
4. Child health -immunization status, episodes of diarrhea, breastfeeding, the use of supplementary foods, prenatal care, and assistance at delivery
5. Marriage and migration
6. Fertility preferences
7. Husband's background and respondent's work
8. Socio-economic indicators
9. Length and weight-measurements of all children 3 through 36 months.

More than in similar fertility and family planning surveys conducted in the past, the SLDHS devoted considerable time and attention to obtaining information on the health status of mothers and children. In addition to many health related questions, anthropometric length and weight measurements were taken on all children 3 months through 36 months.

Cleaning operations
---------------------------

Data were entered onto microcomputers starting just two weeks after the commencement of field work. The ISSA (Integrated System for Survey Analysis) software package of programs developed by IRD/Westinghouse was used for data entry, machine editing, and tabulation. An especially effective procedure for correcting errors and inconsistencies detected during office editing and data entry was to relay information about problems in a questionnaire to the interviewers while they were still in the field. In most cases the problem could be corrected by going back to a respondent. As a result of this procedure, field errors diminished considerabiy With time end the volume af editing was reduced to a minimal level.

Response rate
---------------------------

A total of 8,119 households were listed in seven zones. Not all of these turned out to be valid households in the field and the completion rate (response rate) at the household level was 96.3 percent. From these households, 6,170 eligible respondents were identified and interviews were completed among 5,865 ever-married women for a response rate of 95.1 percent.

It is important to note once again that the districts in the northern and eastern portions of the country were not covered by the SLDHS because of civil disturbances. Whenever comparisons are made between the SLDHS and the earlier SLWFS and SLCPS, the differences in areas covered by the surveys should be kept in mind.

Sampling error estimates
---------------------------

The results from sample surveys are affected by two types of errors: (1) nonsampling error and (2) sampling error. Nonsampling error is due to mistakes made in carrying out field activities, such as failure to locate and interview the correct h0usehold, errors in the way questions are asked, misunderstanding of the questions on the part of either the interviewer or the respondent, data entry errors, etc. Although efforts were made during the design and implementation of the Sri Lanka Demographic and Health Survey to minimize this type of error, nonsampling errors are impossible to avoid entirely and difficult to evaluate statistically.

Sampling errors, on the other hand, can be evaluated statistically. The sample of women ~selected in the SLDHS is only one of many samples of the same size that could have been selected from the same population, using the same design. Each one of these samples would have yielded results somewhat different from the sample that was actually selected. The variability observed between all possible samples constitutes sampling error, which, although it is not known exactly, can be estimated from the survey results.

Sampling error is usually measured in terms of the "standard error" of a particular statistic (mean, percentage, etc.), which is the square root of the variance of the statistic across all possible samples of equal size and design. The standard error can be used to calculate confidence intervals within which one can be reasonably sure the true value of the variable for the whole population falls. For example, for any given statistic calculated from a sample survey, the value of that same statistic as measured in 95 percent of all possible samples of identical size and design will fall within a range of plus or minus two times the standard error of that statistic.

If simple random sampling had been used to select women for the SLDHS, it would have been possible to use straightforward formulas for calculating sampling errors. However, the SLDHS sample design depended on stratification, stages, and clusters and consequently, it was necessary to utilize more complex formulas. The computer package CLUSTERS was used to assist in computing the sampling errors with the proper statistical methodology.

In addition to the standard errors, CLUSTERS computes the design effect (DEFT) for each estimate, which is defined as the ratio between the standard error using the given sample design and the standard error that would result if a simple random sample had been used. A DEFT value of one indicates that the sample design is as efficient as a simple random sample and a value greater than one indicates the increase in the sampling error due to the use of a more c0mplex and less statistically efficient design.

Sampling errors are presented in Table A.1 of the survey Final Report for 32 variables considered to be of major interest. Results are presented for the whole country, for urban and rural areas, for three age groups, and for the seven zones. For each variable, the type of statistic (mean, proportion) and the base population (all women, currently married women) are given in Table A.1. For each variable, Table A.I presents the value of the statistic, R, its standard error, SE, the actual number of cases, N, the weighted number of cases, WN, the DEFT value, and the relative standard error, SE/R. In addition to these indicators, for the entire country ROH and the 95 percent confidence limits, R-2SD and R+2SD are presented. ROH is is a measure of homogeniety. A value of ROH closer to zero indicates more homogeniety in the cluster.

In general, the sampling errors for the country as a whole are small, which means that the SLDHS results are reliable. For example, for the variable children ever born, the overall average from the sample is 3.009 and its standard error is 0.030. Therefore, to obtain the 95 percent confidence limits~ one adds and subtracts twice the standard error to the sample estimate, i.e., 3.009 +-(2 * 0.030), which means that there is a high probability (95 percent) that the true average nnmher of children ever born for all Sri Lankan women falls within the interval of 2.949 to 3.069. This same type of calculation can be made for any other of the variables listed.

摘要
---------------------------

斯里兰卡人口与健康调查（DHS）是过去十年左右斯里兰卡开展的一系列调查中的重要一环。作为国际调查项目的一部分，并参照备受赞誉的世界生育调查（WFS）项目模式设计，DHS为估计斯里兰卡国内时间趋势以及进行跨国比较提供了极为宝贵的数据来源。

调查主要关注生育、避孕和儿童死亡率，与WFS的调查重点一致，但同时也测量了多个儿童健康指标，特别是免疫接种覆盖率和营养状况。纳入卫生部门信息得到了欢迎和成效，因为改善营养状况是斯里兰卡政府高度重视的议题。

斯里兰卡人口与健康调查的目标如下：
1. 为政策制定者和行政管理人员提供关于生育、发病率、家庭规划和健康状况选定指标的当前和准确数据，这些数据可用于制定新的人口福祉战略等；
2. 提供可用于分析时间趋势的数据。SLDHS考察了许多早期调查中涉及的同生育、死亡和健康问题，特别是SLWFS和较近的SLCPS；以及
3. 为国际数据集增加可用于比较研究的资料。

地理覆盖范围
---------------------------

全国

分析单位
---------------------------

- 家庭
- 15-49岁女性

总体
---------------------------

原则上，样本设计旨在涵盖样本区域的私人家庭。居住在机构和机构家庭的人口被排除在外。对于详细个体访谈，合格标准为：前一天晚上在该家庭中住宿的已婚、离婚、分居或丧偶的15至49岁女性。

数据类型
---------------------------

样本调查数据

抽样程序
---------------------------

调查样本设计

基于社会经济和生态标准，以及SLWFS的经验，创建了九个区域。人们认为，六个SLWFS区域中的某些区域过于同质化，应重新绘制，如图i.i所示并如下所述：

区域1 - 科伦坡大都会区，包括SLWFS区域1和区域2的部分地区。
区域2 - 科伦坡支路地区和SLWFS区域2的北部。
区域3 - 西南沿海低地，对应SLWFS区域2的南部。
区域4 - 下南中央山区，对应SLWFS区域6的西部和南部，不包括有大量种植园的区县。
区域5 - 南中央山区，对应SLWFS区域5的部分地区，有大量种植园。
区域6 - 灌溉干旱区，对应SLWFS区域3，有主要或次要灌溉工程。
区域7 - 雨养干旱区，覆盖SLWFS区域3的其余地区。
区域8 - 东部沿海地带，对应SLWFS区域4（不包括在SLDNS中）。
区域9 - 北部省，对应SLWFS区域5（不包括在SLDHS中）。

SLDHS对SLWFS区域所做的更改旨在：a) 将科伦坡城市支路地区与农村腹地分开；b) 将以种植园人口为主的农村地区与其他农村地区分开；以及c) 将灌溉干旱区的新定居点和依赖雨水灌溉的地区的开发项目区分开来。

尽管调查最初计划在所有九个区域进行访谈，但第9区和第8区（北部和东部省）的民事动乱阻止了在该地区进行访谈。这些区域占1986年斯里兰卡估计人口的约14％，已被排除在SLDHS之外。

除了区域5外，样本在区域之间平均分配，每个区域的估计目标为900次完成的个人访谈。区域5被分配更大的目标样本量1350，以允许对种植园工人进行过度抽样。

原则上，样本设计旨在涵盖样本区域的私人家庭。居住在机构和机构家庭的人口被排除在外。对于详细个体访谈，合格标准为：前一天晚上在该家庭中住宿的已婚、离婚、分居或丧偶的15至49岁女性。

对于区域单位的选取，样本框基于1981年人口和住房普查的街区统计数据。然而，这些数据尽可能基于与1985-86劳动力调查有关的工作进行了更新。这特别适用于干旱区灌溉工程开发的新定居地区。在调查之前，对所选街区内的家庭名单进行了更新，以选择最终区域单位内的住房单位。

SLDHS创建的区域旨在捕捉相对同质的人口子群体，作为主要层。每个区域进一步分层为（多达）三个层：城市、农村和种植园地区。通过根据行政和地理位置对抽样区域进行排序，实现了进一步的隐式分层。在所有阶段，包括选择住房单位，都遵循了类似的系统抽样程序。

住房单位的抽样根据层进行两个或三个阶段。在人口密集的区域i、2和3以及所有区域的城区层，使用了三阶段设计：

在第一阶段，根据规模比例（PPS）选择了具有相似特征的地区（waras或种植园）的分层样本。在区域5中，选定的初级抽样单位（PSI）为54个，在其他每个区域中为36个。在给定区域中，要选择的数量按层人口成比例分配。

1. 在每个PSU内，使用PPS系统地无替换地选择两个街区。
2. 最后阶段由选择选定街区中的住房单位组成，使用逆PPS，以便在每个层内产生自加权样本。

对于主要调查，没有进一步的抽样，因为每个选定住房单位中所有合格女性都被纳入样本。此外，对于人体测量测量，所有合格女性的3至36个月大的儿童都被纳入样本。

在区域3至7的非城市层中，程序上的唯一区别是一般情况下每个PSU只选择一个街区。此程序有效地将阶段数量减少到两个：街区作为第一阶段，住房单位作为第二阶段。

由于区域分配了大致相同的样本量，因此整体抽样比例与区域人口成反比。

抽样偏差
---------------------------

再次需要注意的是，由于民事动乱，该国的北部和东部地区的区县未涵盖在SLDHS中。在比较SLDHS与早期的SLWFS和SLCPS时，应记住调查覆盖区域的不同。

数据收集方式
---------------------------

面对面

研究工具
---------------------------

斯里兰卡人口与健康调查使用了两个问卷，每个问卷都进行了预测试。

a) 第一个，称为家庭问卷，用于列出所有通常居住在家庭中的成员以及前一天晚上在家庭中住宿的任何访客。对于列出的每个人，记录了年龄、性别、婚姻状况以及他/她前一天晚上是否在家庭中住宿的信息。从这个名单中选择了合格的受访者进行访谈。合格的受访者定义为目前已婚、离婚、分居或丧偶的15至49岁女性，前一天晚上在家庭中住宿。

b) 第二个或个人问卷针对每个合格受访者进行。平均而言，个人访谈大约需要35至40分钟。个人问卷由九个部分组成：
1. 受访者背景
2. 出生历史-所有活产婴儿和婴儿及儿童死亡日期
3. 避孕-知识、以往使用、当前使用以及过去5年内间隔生育的详细历史
4. 儿童健康-免疫接种状况、腹泻病例、母乳喂养、补充食品的使用、产前护理和分娩时的帮助
5. 婚姻和迁移
6. 生育偏好
7. 丈夫的背景和受访者的工作
8. 社会经济指标
9. 所有3至36个月大儿童的长度和重量测量。

与过去进行的类似生育和家庭规划调查相比，SLDHS在获取有关母亲和儿童健康状况的信息方面投入了更多的时间和精力。除了许多与健康相关的问题外，还对3个月至36个月的儿童进行了人体测量长度和重量测量。

数据清理操作
---------------------------

数据在实地工作开始后的两周内开始输入到微计算机中。IRD/Westinghouse开发的ISSA（综合调查分析系统）软件包用于数据输入、机器编辑和制表。在办公室编辑和数据输入期间发现错误和不一致时，特别有效的纠正错误和不一致的程序是将问卷中的问题信息在访谈者仍在实地时传达给他们。在大多数情况下，问题可以通过返回受访者来纠正。因此，随着时间推移，实地错误大大减少，编辑量降至最低水平。

响应率
---------------------------

在七个区域中列出了8,119个家庭。并非所有这些家庭在实地中都有效，家庭层面的完成率（响应率）为96.3％。从这些家庭中确定了6,170名合格受访者，并在5,865名已婚女性中完成了访谈，响应率为95.1％。

再次需要注意的是，由于民事动乱，该国的北部和东部地区的区县未涵盖在SLDHS中。在比较SLDHS与早期的SLWFS和SLCPS时，应记住调查覆盖区域的不同。

抽样误差估计
---------------------------

样本调查的结果受两种类型的误差的影响：（1）非抽样误差和（2）抽样误差。非抽样误差是由于在执行现场活动时出现的错误造成的，例如未能找到和访谈正确的家庭、提问方式错误、访谈者或受访者对问题的误解、数据输入错误等。尽管在设计和管理斯里兰卡人口与健康调查时努力最大限度地减少此类错误，但非抽样误差无法完全避免，也很难从统计上进行评估。

另一方面，抽样误差可以通过统计方法进行评估。在SLDHS中选择的女性样本只是从同一人口中可能选择的许多相同大小的样本之一。每个这样的样本都会产生与实际选定的样本略有不同的结果。所有可能样本之间观察到的变异性构成了抽样误差，尽管它不完全为人所知，但可以从调查结果中估计出来。

抽样误差通常用特定统计量（均值、百分比等）的“标准误差”来衡量，它是所有可能样本的统计量方差的开方。标准误差可用于计算置信区间，在此区间内，可以合理地确信整个变量的真实值。例如，对于从样本调查中计算出的任何给定统计量，该统计量在所有可能的相同大小和设计样本中的测量值将在加减两倍标准误差的范围内。