The primary objective of the Cambodia National Health Survey is to provide the Ministry of Health with reliable, population-based, nationally representative data or infant/child mortality, fertility, and related health service indicators.
A secondary objective was to provide the ADB-financed Basic Helath Services Project (BHSP) and the World Bank finaced Cambodia Disease Control and Health Development Project (CDCP) with baseline information about their respective Project areas, against which project impact could later be assessed.
Sample Design and Selection
The NHS sample was designed to provide estimates of kwy health indicators including infant/ child mortality rates and fertility rates for the country as a whole, for urban and rural residence, and for the two project catchment areas (the Basic Health Services Project and the Cambodia Disease Control and Health Development Project). In addition, the design allows for estimates of most key variables (but not for the vaccination coverage of children, fertility rates, or mortality rates) for 14 Provinces. In the other Provinces, the sample size is not sufficiently large to allow for province-level estimates. In order to provide sufficient cases to meet the survey objectives, the number of households selected in the NHS sample from each Province was disproportional to the size of the population in the Province. The above arrangements imply stratification into 40 strata, with 40 different sampling fractions. These strata are 20 Provinces, each divided into an urban and a rural sector. As a result, the NHS sample is self-weighting within strata; weights are only necessary when making estimates across more than one stratum.
For a more complete description of the NHS sample design, see Appendix A of the survey final report.
A total of 7,654 women were identified as eligible to be interviewed. Questionnaires were completed for 7,630 of those women, a response rate of 99.7 precent. There is a little difference between the household and individual response rates in urban and rural areas. The same is true for the two project areas.
Dates of collection
Mode of data collection
The NHS involved two types of questionnaires: a household questionnaire and an individual questionnaire. The household questionnaire was administered to all selected households; the individual questionnaire was administered to all women aged 15-49 identified in the household questionnaire as either usual residents of the household or visitors who stayed there on the night before the day of interview. These questionnaires were developed to measure the desired indicators identified by the MOH and Technical Steering Committee. Wording and structure of the questionnaires, where applicable, was based on the model survey instruments Macro International has used in similar surveys worldwide.
The household questionnaire consisted of three parts: 1) a household schedule giving demographic details of all usual household members and overnight visitors; 2) a series of questions relating to the utilization of health services for any household members who had been ill or injured in the past 30 days; and 3) questions about wall and roof materials of the home and household possessions, which in turn were used to compose a measure of overall household socio-economic status.
The individual questionnaire administered to women aged 15-49 gathered detailed information about the woman's reproductive history, and maternal and child health related knowledge and practices. Questions specific to child health practices were limited to children born after January 1993. (i.e., children under age 5)
The questionnaire was developed in English, translated into Khmer, then back translated and corrected. Following this, a three day pretest covering 100 households was conducted in Phnom Penh and rural Kandal Province by twenty interviewers after initial two week training. The questionnaires were finalized following the pretest.
National Institute of Public Health
Ministry of Health, Cambodia
Data Processing was conducted by NIPH with technical assistance form Macro International. The NIPH central office collected questionnaires form supervisors as soon as a cluster was completed. Office editors reviewed questionnaires for consistency and completeness. The data from the questionnaires were then entered and edited on microcomputers using the Integrated System for Survey Analysis (ISSA), a software package developed especially for such surveys by Macro International. During the machine entry, all questionnaires were reentered for verification. Entry and editing of data began one week after the fieldwork started and was completed by the beginning of August 1998.
To provide feedback for the field teams, quality tables were produced every two weeks during the fieldwork. These tables were designed to identify major systematic errors in data collection (e.g. age displacement). The fieldwork coordinators reviewed these tables and, if they found a problem, notified and advised all teams of the steps to be taken to avoid this problem in the future.
A tabulation plan was developed prior to data processing and reviewed and approved by the Technical Steering Committee. Upon completion of data entry and editing, a clean data file was imported into SPSS and a set of preliminary tabulations produced. These were reviewed and discussed by the NIPH Technical Steering Committee and, where necessary, additional tabulations were made to clarify the preliminary findings.
Analysis of the tables and drafting of the survey report was done by the NIPH, Macro International and the ADB Unit of the MOH Project Coordination Unit. The draft report was reviewed by the Technical Steering Committee prior to submission to the Ministry of Health.
The estimate from a sample survey is affected by two types of errors: 1) nonsampling errors, and 2) sampling errors. Nonsampling errors are the results of mistake 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 National Health Survey (NHS) to minimize this type of error, nonsampling errors are impossible to avoid and difficult to evaluate statistically.
Sampling error, on the other hand, can be evaluated statistically. The sample of respondents selected in the NHS 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 between all possible samples. Although the degree of variability is nor known exactly, it can be estimated from the survey results.
A 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 reasonably be assumed to fall. For example, for any given statistic calculated from a sample survey, the value of that statistics will fall within a range of plus or minus two times the standard error of that statistic in 95 percent of all possible sample 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 NHS sample is the result of a multi-stage stratified design and consequently, it was necessary to use more complex formulae. The computer software used to calculate sampling errors for the NHS is the ISSA Sampling Error Module. This module used the Taylor linearization method of variance estimation for survey estimates that are means of proportions. The Jackknife repeated replication method is used for variance estimation of more complex statistics such as fertility and mortality rates.
For details of sampling error estimations information see Appendix B of the final survey report.
Other forms of data appraisal
Data Quality Tables
- Household age distribution
- Births by calendar year
- Reporting of age at death in days
- Reporting of age at death in months
Note: See detailed tables in APPENDIX C of the survey report.
Use of the dataset must be acknowledged using a citation which would include:
- 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
Cambodia Ministry of Health, National Institute of Public Health. Cambodia National Health Survey 1998. Ref. KHM_1998_IDHS_v01_M. Dataset downloaded from http://www.measuredhs.com/what-we-do/survey/survey-display-139.cfm on [date].
Disclaimer and copyrights
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.
Data and Data Related Resources
World Bank, Development Economics Data Group
Generation of DDI documentation
Version 01 (September 2013). Metadata in this DDI is excerpted from "Cambodia National Health Survey 1998" Report.