Technical Notes on the 1998 National and Demographic and Health Survey (NDHS)

Release Date: 

Friday, May 28, 2010


The 1998 National Demographic and Health Survey (NDHS) was a national-level sample survey designed to provide information on various demographic and maternal and child health issues in the Philippines.  The NDHS was conducted by the National Statistics Office (NSO) in collaboration with the Department of Health.  Macro International Inc. of Calverton, Maryland provided technical assistance to the project as part of its international Demographic and Health Surveys program, while financial assistance was provided by the U.S. Agency for International Development (USAID)/Philippines.

This report presents the preliminary results for some of the principal topics covered in the survey.  A more comprehensive and detailed report is scheduled to be published in early 1999.  The final figures are not expected to differ substantially from the findings presented in this preliminary report; however, the results presented here should be regarded as provisional and subject to modification.  In order to examine trends, the survey data have been compared with previous data, especially with information from the 1993 National Demographic Survey.


The primary objective of the NDHS is to provide up-to-date information on fertility and childhood mortality levels; nuptiality; fertility preferences; awareness, approval, and use of family planning methods; breastfeeding practices; and maternal and child health.  This information is intended to assist policy makers and program managers in evaluating and designing programs and strategies for improving health and family planning services in the country.


The main objective of the 1998 NDHS is to provide estimates for each of the sixteen regions of the country with an acceptable precision for socio-demographic characteristics like fertility, family planning use, and health and mortality indicators. The NDHS sample design consisted in selecting some 12,500 households in 755 sample enumeration areas (EAs) which was expected to produce completed interviews with approximately 15,000 women age 15-49. The sample was allocated to each of the regions using the “power allocation”. Within each region, a self-weighting sampling scheme was adopted; however, due to the non-proportional allocation of the sample to the regions, the NDHS sample is not self-weighting at the national level and weighting factors have been applied to the data in this report.

The 1998 NDHS sample is a subsample of the new master sample--the Integrated Survey of Households (ISH) of the NSO.  The expanded sample of ISH consists of 3,416 enumeration areas selected from the 1995 Census frame with a sophisticated design that allows for regional estimates with periodic rotation of panels.  The ISH expanded sample was drawn, first, by selecting barangays systematically with probability proportional to size. In barangays that consist of more than one EA, a subsequent step consisted of selecting the sample EA systematically with probability proportional to size.  Because the primary sampling units in the ISH were selected with probability proportional to size, the EAs for the NDHS were subselected from the ISH with equal probability to make the NDHS selection equivalent to selection with probability proportional to size.  A total of 755 primary sampling units were utilized for the NDHS.  Fieldwork in three sample points was not possible, so a total of 752 points were covered.

NSO conducted a household listing operation in all the NDHS sample points in November 1997 which served as the frame for the selection of the sample households.  A different scheme for selecting sample households was applied to urban and rural areas.  A systematic sampling of households was carried out in urban areas in order to spread the NDHS sample throughout the sampled EA, while compact clustering was employed in rural areas in order to facilitate field operations.  This was accomplished by taking a specified number of consecutive households starting with a household selected at random.


Three types of questionnaires were used for the NDHS: a Household Questionnaire, a Woman's Questionnaire, and a Health Questionnaire.  The contents of the first two questionnaires were based on the DHS Model A Questionnaire, which is designed for use in countries with relatively high levels of contraceptive use.  These model questionnaires were adapted for use in the Philippines during a series of meetings with representatives from the Department of Health, the University of the Philippines Population Institute (UPPI), the Commission on Population (POPCOM), the Food and Nutrition Research Institute (FNRI), USAID/Philippines, and Macro International Inc. Draft questionnaires were then circulated to other interested groups. The questionnaires were developed in English and then translated into and printed in six of the most widely spoken languages in the Philippines (Tagalog, Bicol, Cebuano, Hiligaynon, Ilocano, and Waray).

The Household Questionnaire was used to list all the usual members and visitors in the selected households.  Some basic information was collected on the characteristics of each person listed, including his/her age, sex, education, and relationship to the head of the household.  The main purpose of the Household Questionnaire was to identify women who were eligible for individual interview.  In addition, information was collected about the dwelling itself, such as the source of water, type of toilet facilities, materials used to construct the house, ownership of various consumer goods, and use of iodized salt.

The Woman's Questionnaire was used to collect information from women age 15-49.  These women were asked questions on the following topics:

  • Background characteristics (age, education, religion, etc.),
  • Reproductive history,
  • Knowledge and use of family planning methods,
  • Prenatal, delivery, and postnatal care,
  • Breastfeeding and weaning practices,
  • Vaccinations and health of children under age five,
  • Marriage,
  • Fertility preferences,
  • Husband's background and respondent's work,
  • Mortality of her brothers and sisters.

The Health Questionnaire was developed in close collaboration with the Department of Health in partial substitution for the cancelled National Health Survey.  It included questions on garbage collection, utilization of and satisfaction with various types of health facilities, knowledge concerning several herbal medicines, and health insurance coverage. 


The NDHS questionnaires were pretested in October 1997.  Female interviewers were trained at the NSO central office in Manila, after which they conducted interviews in various locations in the field under the observation of staff from NSO central office.  Altogether, approximately 160 Household, Woman's and Health Questionnaires were completed.  Based on observations in the field and suggestions made by the pretest field teams, revisions were made in the wording and translations of the questionnaires.

Training for the main survey took place in two phases.  In the first phase, approximately 35 trainers from NSO, DOH, UPPI, and POPCOM gathered for two weeks in late January at a training center near the NSO central office in Manila.  They received thorough training in how to fill and edit the questionnaires, how to supervise fieldwork, and how to train field staff in their respective training sites.  These trainers then dispersed to the six training sites (Agoo, Malolos, Lucena City, Cebu City, Iloilo City, and Davao City) where they trained some 261 interviewers, 44 supervisors, and 43 field editors for three weeks (February 9-27, 1998). Initially, training consisted of lectures on how to complete the questionnaires, with mock interviews between participants to gain practice in asking questions. Towards the end of the training course, the participants spent several days in practice interviewing in households near the training sites.

Fieldwork for the NDHS was carried out by 44 interviewing teams.  Each team, except that which covered Palawan, Lanao del Sur and Maguindanao, consisted of 1 supervisor, 1 field editor, and 3-7 female interviewers, for a total of 348 field staff.  Fieldwork commenced on 3 March 1998 and was completed in the first week of May 1998. Periodic field monitoring of the NDHS operations was done by the NSO regional and provincial officials, NDHS regional supervisor and selected NSO central office staff.


All questionnaires for the NDHS were returned to Manila for data processing at NSO headquarters.  The processing operation consisted of office editing, coding of open-ended questions, data entry, and editing inconsistencies found by the computer programs.  The data were processed on 18 microcomputers working in double shifts.  The DHS data entry and editing programs were written in ISSA (Integrated System for Survey Analysis).  Data processing commenced in mid-March  and was completed by the end of June 1998.


Table 1 shows response rates for the survey and reasons for non-response.  A total of 13,708 households was selected for the sample, of which 12,407 were successfully interviewed.  The shortfall is primarily due to dwellings that were vacant or in which the inhabitants had left for an extended period at the time they were visited by the interviewing teams.  Of the 12,567 households occupied, 99 percent were successfully interviewed.

In these households, 14,390 women were identified as eligible for the individual interview (i.e., age 15-49) and interviews were completed for 13,983 or 97 percent of them.  The principal reason for non-response among eligible women was the failure to find them at home despite repeated visits to the household.  The refusal rate was low.