The 2008 Nigeria Demographic Health Survey (NDHS) is a nationally representative survey of 33,385 women age 15-49 and 15,486 men age 15-59. The 2008 NDHS is the fourth comprehensive survey conducted in Nigeria as part of the Demographic and Health Surveys (DHS) programme. The data are intended to furnish programme managers and policymakers with detailed information on levels and trends in fertility; nuptiality; sexual activity; fertility preferences; awareness and use of family planning methods; infants and young children feeding practices; nutritional status of mothers and young children; early childhood mortality and maternal mortality; maternal and child health; and awareness and behaviour regarding HIV/AIDS and other sexually transmitted infections. Additionally, the 2008 NDHS collected information on malaria prevention and treatment, neglected tropical diseases, domestic violence, fistulae, and female genital cutting (FGC).
The 2008 Nigeria Demographic and Health Survey (2008 NDHS) was implemented by the National Population Commission from June to October 2008 on a nationally representative sample of more than 36,000 households. All women age 15-49 in these households and all men age 15-59 in a sub-sample of half of the households were individually interviewed.
While significantly expanded in content, the 2008 NDHS is a follow-up to the 1990, 1999, and 2003 NDHS surveys and provides updated estimates of basic demographic and health indicators covered in these earlier surveys. In addition, the 2008 NDHS includes the collection of information on violence against women. Although previous surveys collected data at the national and zonal levels, the 2008 NDHS is the first NDHS survey to collect data on basic demographic and health indicators at the state level.
The primary objectives of the 2008 NDHS project were to provide up-to-date information on fertility levels; nuptiality; sexual activity; fertility preferences; awareness and use of family planning methods; breastfeeding practices; nutritional status of mothers and young children; early childhood mortality and maternal mortality; maternal and child health; and awareness and behaviour regarding HIV/AIDS and other sexually transmitted infections.
The survey results show fertility in Nigeria has remained at a high level over the last 17 years from 5.9 births per woman in 1991 to 5.7 births in 2008. On average, rural women are having two children more than urban women (6.3 and 4.7 children, respectively). Fertility differentials by education and wealth are noticeable. Women who have no formal education and women in the lowest wealth quintile on average are having 7 children, while women with higher than a secondary education are having 3 children and women in the highest wealth quintile are having 4 children.
In the 2008 NDHS, 72 percent of all women and 90 percent of all men know at least one contraceptive method. Male condoms, the pill, and injectables are the most widely known methods.
Twenty-nine percent of currently married women have used a family planning method at least once in their lifetime. Fifteen percent of currently married women are using any contraceptive method and 10 percent are using a modern method. The most commonly used methods among currently married women are injectables (3 percent), followed by male condoms and the pill (2 percent each).
Current use of contraception in Nigeria has increased from 6 percent in 1990 and 13 percent in 2003 to 15 percent in 2008. There has been a corresponding increase in the use of modern contraceptive methods, from 4 percent in 1990 and 8 percent in 2003 to 10 percent in 2008.
Data from the 2008 NDHS indicate that the infant mortality rate is 75 deaths per 1,000 live births, while the under-five mortality rate is 157 per 1,000 live births for the five-year period immediately preceding the survey. The neonatal mortality rate is 40 per 1,000 births. Thus, almost half of childhood deaths occurred during infancy, with one-quarter taking place during the first month of life.
Child mortality is consistently lower in urban areas than in rural areas. There is also variation in the mortality level across zones. The infant mortality and under-five mortality rates are highest in the North East, and lowest in the South West.
In Nigeria, children are considered fully vaccinated when they receive one dose of BCG vaccine, three doses of DPT vaccine, three doses of polio vaccine, and one dose of measles vaccine. Overall, 23 percent of children 12-23 months have received all vaccinations at the time of the survey. Fifty percent of children have received the BCG vaccination, and 41 percent have been vaccinated against measles. The coverage of the first dose of DPT vaccine and polio 1 is 52 and 68 percent, respectively). However, only 35 percent of children have received the third dose of DPT vaccine, and 39 percent have received the third dose of polio vaccine. A comparison of the 2008 NDHS results with those of the earlier surveys shows there has been an increase in the overall vaccination coverage in Nigeria from 13 percent in 2003 to the current rate of 23 percent. However, the percentage of children with no vaccinations has not improved for the same period, 27 percent in 2003 and 29 percent in 2008.
In Nigeria more than half of women who had a live birth in the five years preceding the survey received antenatal care from a health professional (58 percent); 23 percent from a doctor, 30 percent from a nurse or midwife, and 5 percent from an auxiliary nurse or midwife. Thirty-six percent of mothers did not receive any antenatal care.
Tetanus toxoid injections are given during pregnancy to prevent neonatal tetanus. Overall, 48 percent of last births in Nigeria were protected against neonatal tetanus.
More than one-third of births in the five years before the survey were delivered in a health facility (35 percent). Twenty percent of births occurred in public health facilities and 15 percent occurred in private health facilities. Almost two-thirds (62 percent) of births occurred at home. Nine percent of births were assisted by a doctor, 25 percent by a nurse or midwife, 5 percent by an auxiliary nurse or midwife, and 22 percent by a traditional birth attendant. Nineteen percent of births were assisted by a relative and 19 percent of births had no assistance at all. Two percent of births were delivered by a caesarean section.
Overall, 42 percent of mothers received a postnatal check-up for the most recent birth in the five years preceding the survey, with 38 percent having the check-up within the critical 48 hours after delivery.
Results from the 2008 NDHS show that the estimated maternal mortality ratio during the seven-year period prior to the survey is 545 maternal deaths per 100,000 live births.
BREASTFEEDING AND NUTRITION
Ninety-seven percent of Nigerian children under age five were breastfed at some point in their life. The median breastfeeding duration in Nigeria is long (18.1 months). On the other hand, the median duration for exclusive breastfeeding is only for half a month. A small proportion of babies (13 percent) are exclusively breastfed throughout the first six months of life. More than seven in ten (76 percent) children age 6-9 months receive complementary foods. Sixteen percent of babies less than six months of age are fed with a bottle with a nipple, and the proportion bottle-fed peaks at 17 percent among children in the age groups 2-3 months and 4-5 months.
Anthropometric measurements carried out at the time of the survey indicate that, overall, 41 percent of Nigerian children are stunted (short for their age), 14 percent are wasted (thin for their height), and 23 percent are underweight. The indices show that malnutrition in young children increases with age, starting with wasting, which peaks among children age 6-8 months, underweight peaks among children age 12-17 months, and stunting is highest among children age 18-23 months. Stunting affects half of children in this age group and almost one-third of children age 18-23 months are severely stunted.
Overall, 66 percent of women have a body mass index (BMI) in the normal range; 12 percent of women are classified as thin and 4 percent are severely thin. Twenty-two percent of women are classified as overweight or obese, with 6 percent in the latter category.
Seventeen percent of all households interviewed during the survey had at least one mosquito net, while 8 percent had more than one. Sixteen percent of households had at least one net that had been treated at some time (ever-treated) with an insecticide. Eight percent of households had at least one insecticide-treated net (ITN).
Mosquito net usage is low among young children and pregnant women, groups that are particularly vulnerable to the effects of malaria. Overall, 12 percent of children under five slept under a mosquito net the night before the survey. Twelve percent of children slept under an ever-treated net and 6 percent slept under an ITN. Among pregnant women, 12 percent slept under any mosquito net the night before the interview. Twelve percent slept under an ever-treated net and 5 percent slept under an ITN.
Among women who had their last birth in the two years before the survey, 18 percent took an anti-malarial drug during the pregnancy. Eleven percent of all pregnant women took at least one dose of a sulphadoxine-pyrimethamine (SP) drug such as Fansidar, Amalar, or Maloxine, while 7 percent reported taking two or more doses of an SP drug. Eight percent of the women who took an SP drug were given the drug during an antenatal care visit, a practice known as intermittent preventive treatment (IPT).
HIV/AIDS KNOWLEDGE AND BEHAVIOUR
The majority of women (88 percent) and men (94 percent) age 15-49 have heard of HIV or AIDS. However, only 23 percent of women and 36 percent of men have what can be considered comprehensive knowledge about the modes of HIV transmission and prevention. Comprehensive knowledge means knowing that using condoms and having just one uninfected, faithful partner can reduce the chance of getting HIV, knowing that a healthy-looking person can have HIV, and rejecting the two most common local misconceptions about HIV transmission or prevention, that HIV and AIDS can be transmitted through supernatural means or through mosquito bites.
Fifty-two percent of women and 59 percent of men age 15-49 know that HIV can be transmitted through breastfeeding. Twenty-eight percent of women and 39 percent of men know that the risk of mother-to-child transmission (MTCT) can be reduced by the mother taking special drugs during pregnancy.
Given that most HIV cases in Nigeria occur as a result of heterosexual contact, information about the level of higher-risk sexual intercourse (i.e., sexual intercourse with a non-marital, non-cohabiting partner) in the past 12 months is important for planning HIV prevention programmes. The 2008 NDHS findings indicate that 1 percent of women and 10 percent of men had two or more sexual partners during the 12 months preceding the survey. Ten percent of women and 23 percent of men had higher-risk sexual intercourse in this period. Among these respondents, only 33 percent of women and 54 percent of men reported that they used a condom the last time they had sexual intercourse with a higher-risk sexual partner.
Among the adult population age 15-49, 17 percent of women and 15 percent of men have been tested for HIV at some time. Seven percent of women and 7 of men received the results from their last HIV test that was taken in the past 12 months.
One eligible woman in each household was asked questions on domestic violence. In Nigeria, domestic violence occurs across all socioeconomic and cultural backgrounds. Twenty-eight percent of all women reported experiencing physical violence since the age of 15, and 15 percent of women experienced physical violence in the 12 months preceding the survey. Among women who experienced violence since age 15, a total of 45 percent reported that their current husband or partner was the perpetrator and 7 percent reported that the perpetrator was a former husband or partner.
Overall, 7 percent of women reported that they had experienced sexual violence at some time in their lives. Forty-three percent of women reported that their first experience with sexual intercourse occurred when they were less than 20 years of age. Half of women reported that their current or former husband, partner, or boyfriend committed the act of sexual violence. It is important to highlight that among women who were younger than age 15 when they first experienced sexual violence, 28 percent reported that the perpetrator was a stranger, 12 percent reported that the person was a friend or acquaintance, 11 percent reported that the person was a relative, and 7 percent reported that the person was a family friend.
Thirty-four percent of Nigerian women who ever experienced physical or sexual violence sought help to stop the violence. Eight percent of abused women did not seek help but did tell someone about the violence, and 45 percent of the women did not seek help from any source and did not tell anyone about the violence.
ORPHANS AND VULNERABLE CHILDREN
Twelve percent Nigerian children under age 18 in the households sampled in the 2008 NDHS were not living with a biological parent. Six percent of children under age 18 are orphaned, that is, one or both parents are dead.
Earlier NDHS surveys obtained information on orphanhood only for children under age 15. A comparison of the results from the 2003 and 2008 surveys for this age group indicates that there has been a slight decrease in orphanhood from 6.2 percent to 5.2 percent. The proportion of children who are not living with either parent decreased from 11 to 9 percent for children under age 15.
Overall, 5 percent of children under age 18 are considered vulnerable, i.e., they live in a household in which at least one adult was chronically ill for three months during the past 12 months, or they had a parent living in the household (or elsewhere) who had experienced chronic illness in the past year. Overall, 11 percent of children under age 18 are considered orphans and/or vulnerable.
Kind of Data
Sample survey data
Unit of Analysis
- Women age 15-49
- Men age 15-59
- Children under six years
The Nigeria Demographic and Health Survey 2008 covers the following topics:
- Alcohol Consumption
- Birth Registration
- Causes of Death
- Domestic Violence
- Female Genital Cutting
- Fistula Questions
- GPS/Georeferenced–Global Positioning System or Georeferenced Data
- HIV Behavior
- HIV Knowledge–Questions assess knowledge/sources of knowledge/ways to avoid HIV
- Iodine salt test
- Malaria Module (bednets)
- Malaria/Bednet Questions
- Maternal Mortality
- Men's Survey
- Social Marketing
- TB Questions
- Tobacco Use
- Verbal Autopsy
- Women's Status–Questions: women's autonomy (household decisionmaking/free movement/access money) & Dom. violence
The 2008 Nigeria Demographic Health Survey (NDHS) is a nationally representative survey. The sample design allowed for specific indicators, such as contraceptive use, to be calculated for each of the 6 zones and 37 states (36 states plus the Federal Capital Territory, Abuja).
The population covered by the 2008 DHS is defined as the universe of all women age 15-49 who were either permanent residents of the households in the 2008 NDHS sample or visitors present in the households on the night before the survey were eligible to be interviewed. In a sub-sample of half of the households, all men age 15-59 who were either permanent residents of the households in the 2008 NDHS sample or visitors present in the households on the night before the survey were eligible to be interviewed.
Producers and sponsors
Nigeria. National Population Commission
United States Agency for International Development
U.S. President’s Emergency Plan for AIDS Relief
United Nations Population Fund
The sample for the 2008 NDHS was designed to provide population and health indicators at the national, zonal, and state levels. The sample design allowed for specific indicators, such as contraceptive use, to be calculated for each of the 6 zones and 37 states (36 states plus the Federal Capital Territory, Abuja). The sampling frame used for the 2008 NDHS was the 2006 Population and Housing Census of the Federal Republic of Nigeria conducted in 2006, provided by the National Population Commission (NPC).
Administratively, Nigeria is divided into states. Each state is subdivided into local government areas (LGAs), and each LGA is divided into localities. In addition to these administrative units, during the 2006 Population Census, each locality was subdivided into convenient areas called census enumeration areas (EAs). The primary sampling unit (PSU), referred to as a cluster for the 2008 NDHS, is defined on the basis of EAs from the 2006 EA census frame. The 2008 NDHS sample was selected using a stratified two-stage cluster design consisting of 888 clusters, 286 in the urban and 602 in the rural areas. The final survey sample included 886 instead of 888 clusters. During fieldwork, access was not obtained in one cluster due to flooding, and in another cluster due to inter-communal disturbances). A representative sample of 36,800 households was selected for the 2008 NDHS survey, with a minimum target of 950 completed interviews per state. In each state, the number of households was distributed proportionately among its urban and rural areas.
A complete listing of households and a mapping exercise were carried out for each cluster from April to May 2008, with the resulting lists of households serving as the sampling frame for the selection of households in the second stage. All private households were listed. The NPC listing enumerators were trained to use Global Positioning System (GPS) receivers to take the coordinates of the 2008 NDHS sample clusters.
In the second stage of selection, an average of 41 households was selected in each cluster, by equal probability systematic sampling. All women age 15-49 who were either permanent residents of the households in the 2008 NDHS sample or visitors present in the households on the night before the survey were eligible to be interviewed. In a sub-sample of half of the households, all men age 15-59 who were either permanent residents of the households in the 2008 NDHS sample or visitors present in the households on the night before the survey were eligible to be interviewed. In addition, a sub-sample of one eligible woman in each household was randomly selected to be asked additional questions about domestic violence.
A total of 36,298 households were selected and of these 34,644 were occupied. Of the 34,644 households found, 34,070 were successfully interviewed, yielding a response rate of 98 percent. There is no significant difference between rural and urban areas in terms of response rates.
In the interviewed households, a total of 34,596 women were identified to be eligible for the individual interview, and 97 percent of them were successfully interviewed. For men, 16,722 were identified as eligible in half the households, and 93 percent of them were successfully interviewed.
Dates of Data Collection
Data Collection Mode
Data Collection Notes
The training for the pre-test took place March 3-12, 2008. Thirty-two interviewers (15 females and 17 males) were trained to administer the questionnaires and take anthropometric measurements. The pre-test training for the interviewers and supervisors consisted of a project overview and survey objectives, techniques of interviewing, field procedures, a detailed description of all sections of the household and individual questionnaires, and two days of field practice. The trainers/resource people included professionals from NPC and ICF Macro.
The pre-test was conducted in 6 states by 6 teams March 15-22, 2008. The teams were divided according to languages. There were 2 Hausa teams in the North East and North West zones, 2 English teams in the South South and North Central zones, 1 Yoruba team in the South West, and 1 Igbo team in the South East. The supervisors and editors were drawn from the NPC core technical team. The teams covered 6 zones (one state in each zone) and aimed at completing 25 urban and 25 rural households per state. At the end of fieldwork, a debriefing session was held March 24-25, 2008 in Kaduna with all staff involved in the pre-test, and the questionnaires were amended based on the pre-test findings.
TRAINING OF FIELD STAFF
NPC recruited and trained 368 people for the fieldwork to serve as zonal coordinators, supervisors, field editors, female and male interviewers, reserve interviewers, and quality control interviewers. Training of field staff for the main survey was conducted during a three-week period in May-June 2008. The training course consisted of instruction regarding interviewing techniques and field procedures, a detailed review of items on the questionnaires, instruction and practice in weighing and measuring children, mock interviews between participants in the classroom, and practice interviews with real respondents in areas outside the 2008 NDHS sample points. During this period, field editors, team supervisors, and quality control interviewers were provided with additional training in methods of field editing, data quality control procedures, and fieldwork coordination. Thirty-seven supervisors, 37 editors, 152 female interviewers, and 74 male interviewers were selected to make up 37 data collection teams for the 2008 NDHS. Thirty-seven people were selected to be quality control interviewers.
Thirty-seven interviewing teams carried out data collection for the 2008 NDHS. Each team consisted of 1 supervisor (team leader), 1 field editor, 4 female interviewers, 2 male interviewers, and 2 drivers. Nineteen senior staff members from NPC, designated as zonal coordinators, coordinated and supervised fieldwork activities. Data collection took place over a four-month period from June to October 2008.
National Population Commission
The questionnaire for each DHS can be found as an appendix in the final report for each study.
Three questionnaires were used for the 2008 NDHS. They are the Household Questionnaire, the Women's Questionnaire, and the Men's Questionnaire. These questionnaires were adapted to reflect the population and health issues relevant to Nigeria at a series of meetings with various stakeholders from government ministries and agencies, non-governmental organisations, and international donors. In addition to English, the questionnaires were translated into three major Nigerian languages: Hausa, Igbo, and Yoruba.
a) The Household Questionnaire was used to list all the usual members and visitors of selected households. Some basic information was collected on the characteristics of each person listed, including his or her age, sex, education, and relationship to the head of the household. For children under age 18, survival status of the parents was determined. If a child in the household had a parent who was sick for more than three consecutive months in the 12 months preceding the survey or a parent who had died, additional questions related to support for orphans and vulnerable children were asked. Additionally, if an adult in the household was sick for more than three consecutive months in the 12 months preceding the survey or an adult in the household died, questions were asked related to support for sick people or people in households where a household member has died. The data on the age and sex of household members obtained in the Household Questionnaire was used to identify women and men who were eligible for the individual interview. Additionally, the Household Questionnaire collected information on characteristics of the household's dwelling unit, such as the source of water, type of toilet facilities, materials used for the floor of the house, ownership of various durable goods, and ownership and use of mosquito nets (to assess the coverage of malaria prevention programmes). The Household Questionnaire was also used to record height and weight measurements for children age 0-59 months and women age 15-49.
b) The Women's Questionnaire was used to collect information on all women age 15-49. These women were asked questions on the following main topics:
- Background characteristics (education, residential history, media exposure, etc.)
- Birth history and childhood mortality
- Knowledge and use of family planning methods
- Fertility preferences
- Antenatal, delivery, and postnatal care
- Breastfeeding and infant and young child feeding practices
- Vaccinations and childhood illnesses
- Marriage and sexual activity
- Women's work and husband's background characteristics
- Women's and children's nutritional status
- Malaria prevention and treatment
- Awareness and behaviour regarding HIV/AIDS and other sexually transmitted infections (STIs)
- Adult mortality including maternal mortality
- Women's status and health outcomes
- Domestic violence
- Female genital cutting
c) The Men's Questionnaire was administered to all men age 15-59 in every second household in the 2008 NDHS sample. The Men's Questionnaire collected much of the same information found in the Women's Questionnaire, but was shorter because it did not contain a detailed reproductive history or questions on maternal and child health or nutrition.
All questionnaires for the 2008 NDHS were returned to the NPC headquarters office in Abuja for data processing, which consisted of office editing, coding of open-ended questions, data entry, and editing computer-identified errors. The data were processed by a team of 30 data entry operators, 3 data coders, 4 data entry supervisors, and 8 secondary editors. Data entry and editing were accomplished using the CSPro software. The processing of data was initiated in July 2008 and completed in February 2009.
Estimates of Sampling Error
Sampling errors, on the other hand, can be evaluated statistically. The sample of respondents selected in the 2008 NDHS 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 not 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 used to calculate confidence intervals within which the true value for the population can reasonably be assumed to fall. For example, for any given statistic calculated from a sample survey, the value of that statistic will fall within a range of plus or minus two times the standard error of that statistic in 95 percent of all possible samples 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 2008 NDHS sample is the result of a multi-stage stratified design, and, consequently, it was necessary to use a more complex formula. The computer software used to calculate sampling errors for the 2008 NDHS uses the Taylor linearisation method of variance estimation for survey estimates that are means or proportions. Another approach, the Jackknife repeated replication method, is used for variance estimation of more complex statistics such as fertility and mortality rates.
The Taylor linearisation method treats any percentage or average as a ratio estimate, r = y/x, where y represents the total sample value for variable y, and x represents the total number of cases in the group or subgroup under consideration.
The Jackknife repeated replication method derives estimates of complex rates from each of several replications of the parent sample, and calculates standard errors for these estimates using simple formulas. Each replication considers all but one cluster in the calculation of the estimates. Pseudo-independent replications are thus created. In the 2008 NDHS, there were 886 non-empty clusters. Hence, 886 replications were created.
In addition to the standard error, the design effect (DEFT) for each estimate is also calculated. The design effect 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 1.0 indicates that the sample design is as efficient as a simple random sample, while a value greater than 1.0 indicates the increase in the sampling error due to the use of a more complex and less statistically efficient design. Relative errors and confidence limits for the estimates are also computed.
Sampling errors for the 2008 NDHS are calculated for selected variables considered to be of primary interest for the women's and men's samples. The results are presented in an appendix to the Final Report for the country as a whole, for urban and rural areas, and for 6 regions. For each variable, the type of statistic (mean, proportion, or rate) and the base population are given in Table C.1 of the Final Report. Tables C.2 to C.10 present the value of the statistic (R), its standard error (SE), the number of unweighted (N) and weighted (WN) cases, the design effect (DEFT), the relative standard error (SE/R), and the 95 percent confidence limits (R±2SE), for the selected variables including fertility and mortality rates. The sampling errors for mortality rates except for the entire country are presented for the 10 years preceding the survey. The DEFT is considered undefined when the standard error considering a simple random sample is zero (when the estimate is close to 0 or 1). In the case of the total fertility rate, the number of unweighted cases is not relevant, as there is no known unweighted value for woman-years of exposure to childbearing.
The confidence interval (e.g., as calculated for children ever born to women age 40-49) can be interpreted as follows: the overall average from the national sample is 6.507 and its standard error is 0.057. Therefore, to obtain the 95 percent confidence limits, one adds and subtracts twice the standard error to the sample estimate (i.e., 6.507 ± 2×0.057; in other words between 6.392 and 6.622). There is a high probability (95 percent) that the true average number of children ever born to all women aged 40-49 is between 6.392 and 6.622.
For the women sampling errors and not taking into consideration the estimate for using female sterilisation, the relative standard errors (SE/R) for the means and proportions range between 2 and 8.8 percent, with an average relative standard error of 2.99 percent; the highest relative standard errors are for estimates of very low values (e.g., currently using IUD-1 percent-has 8.8 percent of relative error). So in general, the relative standard error for most estimates for the country as a whole is small, except for estimates of very small proportions. The relative standard error for the total fertility rate is small, 1.4 percent. However, for the mortality rates, the average relative standard error for the past five-year period mortality rates is much higher, about 3.2 percent.
There are differentials in the relative standard error for the estimates of women sub-populations. For example, for the variable want no more children, the relative standard errors as a percent of the estimated mean for the whole country, urban total area and for the rural total area are 2.1 percent, 3.0 percent and 2.7 percent, respectively. For the total women sample, the value of the design effect (DEFT) averaged over all variables is 1.86, which means that due to multi-stage clustering of the sample the average standard error is increased by a factor of 1.86 over that in an equivalent simple random sample.
Non-sampling errors are the results of mistakes 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 2008 Nigeria DHS (2008 NDHS) to minimise this type of error, non-sampling errors are impossible to avoid and difficult to evaluate statistically.
Data and Data Related Resources
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