a School of Nursing, Columbia University, NY, USA.
b NYS Psychiatric Institute and Columbia University, USA
Reprint requests to: Richard Garfield, Columbia University, 630 West 168th Street, Box 6, New York, NY 10032, USA. E-mail: rmg3{at}columbia.edu
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Abstract |
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Methods Four preliminary models, based on unadjusted projections, were developed. A logistic regression model was then developed on the basis of six social variables in Iraq and comparable information from countries in the State of the World's Children report. Missing data were estimated for this model by a multiple imputation procedure. The final model depends on three socio-medical indicators: adult literacy, nutritional stunting of children under 5 years, and access to piped water.
Results The model successfully predicted both the mortality rate in 1990, under stable conditions, and in 1991, following the Gulf War. For 1996, after 5 years of sanctions and prior to receipt of humanitarian food via the oil for food programme, this model shows mortality among children under 5 to have reached an estimated 87 per 1000, a rate last experienced more than 30 years ago.
Conclusions Accurate and timely estimates of mortality levels in developing countries are costly and require considerable methodological expertise. A rapid estimation technique like the one developed here may be a useful tool for quick and efficient estimation of mortality rates among under 5 year olds in countries where good mortality data are not routinely available. This is especially true for countries with complex humanitarian emergencies where information on mortality changes can guide interventions and the social stability to use standard demographic methods does not exist.
Keywords Mortality, humanitarian crisis, demographic surveys, estimation, multiple imputation
Accepted 12 November 1999
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Introduction |
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Background |
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Subsequently, in 1995, a study sponsored by the Food and Agricultural Organization (FAO) in the poor urban neighbourhood of Saddam City in Baghdad calculated a mortality rate among under 5 year olds of 216 per 1000 live births.13 Had mortality risen even higher in 1995 than it was in the post-war period of 1991, when it had already risen nearly threefold? The question was important as no other reliable source was available to estimate current mortality.
The FAO study suffered from serious flaws in methods and interpretation which are common to surveys to assess young child mortality: (1) the study sample was small, including only 2108 children; (2) several of the study clusters showed mortality rates far higher than any other; (3) there were no international team members on some of the field data collection teams; and (4) no field verification checks on data collected were performed.
A follow-up study in 1996 by the Center for Social and Economics Rights (CESR)14 selected 44 newly randomized clusters throughout Baghdad and repeated 20 clusters from the 1995 study. Only 80% of the mothers interviewed in repeat clusters were interviewed the year before. Among these 237 mothers, 96% of all births were confirmed on both surveys but 65 of the 74 deaths reported in 1995 were not reported again in 1996. The 1995 study's conclusions were subsequently withdrawn by the authors,14 but not before national projections from these flawed data were published. Notwithdstanding the retraction of the original data, their estimate of more than 500 000 excess child deaths associated with the embargo has often been repeated by critics of sanctions.
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Changes in Health Status |
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Univariate Models to Estimate Mortality |
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Model 1: Correlating malnutrition and mortality data
Data from the 1996 MICS survey for each of the three measures of malnutrition were compared to the data for all other countries in the State of the World's Children report16 with levels of malnutrition within a range of 10% higher or lower. Eight countries reported a prevalence of low weight-for-age in the range 2026%, 12 countries reported low height-for-age in the range 2834%, and 10 countries reported low weight-for-height among under 5 year olds in the range 911%. The average under 5 mortality rates reported for those countries that shared Iraq's weight-for-age values were 126.1 ± 67.0, for those countries that shared Iraq's height-for-age values were 131.2 ± 76.5, and for those countries that shared Iraq's weight-for-height values were 148.6 ± 64.2. The unweighted average of these three rates is 135.3 ± 69.2 (Table 1). The major weakness in this approach is the assumption that the relationship between mortality and malnutrition in Iraq is likely to be similar to countries with more stable social conditions. While higher malnutrition usually implies higher mortality, the relationship cannot be assumed to be linear and may be heavily influenced by other cultural or social factors.
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Model 3: Comparison with eight malnutrition and mortality studies
Pelletier et al. identified eight observational studies in six countries where weight-for-age assessments were correlated with subsequent mortality rates among under 5 year olds.17 While the log of mortality rates in these eight studies generated nearly parallel slopes of increase as malnutrition increased, the baseline levels of mortality among those with mild malnutrition carried eightfold. Point estimates and confidence intervals for average mortality among under 5 year olds from these eight studies were 11.4 ± 8.3 per 1000 births for those with normal weight, 19.3 ± 16.1 per 1000 among those mildly underweight, 34.4 ± 23.4 per 1000 among those moderately underweight, and 91.4 ± 63.2 per 1000 for those severely underweight. Each of these rates is multiplied by five to derive the cumulative rate of death among under 5 year olds. Multiplying these rates by the proportion of Iraqi children under 5 years with normal weight (42.8%), and who are mildly underweight (34.3%), moderately underweight (16.6%) and severely underweight (6.3%) as determined in the MICS 1996 survey21,22 (see Endnote) generates a mortality rate estimate of 92.0 ± 68.7 deaths per 1000. Limitations in this approach include the imprecision in using as a model data with widely varying values, the wide confidence band generated, and the possibility that malnutrition-mortality dynamics in Iraq may be different from those in the eight countries used to develop this model.
Model 4: Comparison to countries with similar expected population attributable risk
Pelletier et al.18 observed that although mortality rates varied a great deal, the slopes of the increase in the rate of mortality at various levels of malnutrition were nearly parallel. This permits calculation of an equation for the slope of relative risk of mortality and calculation of the population attributable risk (PAR) associated with low weight-for-age. While the actual mortality rate remains unknown, the proportion of all mortality which is attributable to mild, moderate, and severe malnutrition can be calculated. Rates of the PAR varying from 12% to 66% were presented for 53 countries.17 Data on the proportion of under 5-year-old Iraqis with moderate and severe malnutrition were transformed according to equations provided by Pelletier17 and fitted to his regression equation to estimate the PAR for malnutrition in Iraq in 1996. The Iraqi rate of 64% PAR was within a 10% range of only the highest three countries among the 53 presented: Nepal, Bangladesh, and India. Data on the under 5-year-old mortality rate for these three countries was taken from the 1998 State of the World's Children report.16 They averaged 113.0 ± 2.6. Limitations in this approach are similar to those in the first model and the small number of countries upon which this model's comparisons are based.
These four estimates, depending on three independent data sources, consistently demonstrate a trend toward increased mortality. They generate a range of estimates of mortality among under 5 year olds from 74 to 135.
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Regression Modelling |
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Countries with the most complete data sets are a biased sample of all countries, strongly weighted toward higher social indicators and lower mortality rates. Because of this, and the large amount of missing data, imputing those missing values is important.
The multiple imputation procedure of Rubin24 was used to achieve this goal. In this technique, an imputation model is constructed to estimate missing values as a regression function of known variables. These estimates produce a variety of results, including better and worse case scenarios. The bootstrap procedure selects a random sample with replacement from the data with complete records. The desired imputation model is then fitted to the bootstrap sample to derive coefficients of covariates and a set of error terms, where the error term is the observed value minus model predicted value.
Missing data are imputed by substitution of the predicted values. In our data set, the imputation model estimates a missing value on the basis of known values for under 5-year-old mortality rate, the under one-year-old mortality rate and GNP per capita are independent variables. Imputed values, together with the originally complete records, form one complete data set. The process of iteration is repeated to obtain five completed data sets. Rubin24 provides formulae for combining the results to derive point estimates for imputed values as a simple average of the multiple completed-data point estimates, together with confidence intervals.
The rate of mortality among those aged under 5 is considered as the number of events (deaths) per 1000 trials (births). Because values for this dependent variable fall between 0 and 1, linear and log-linear models are inappropriate. We employ a binomial logistic regression model.
Five completed data sets were generated through multiple imputation. For each data set the binomial logistic regression model with six independent variables was fitted to estimate mortality among under 5-yearolds (Table 3). Five estimates,
, ...,
were obtained. The final estimator of under 5-year-old mortality rate is the mathematical average of the five, i.e.:
=
i and variance of
is:
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Only six of the eight potential independent variables were significantly associated with known under 5-year-old mortality rates among the 195 country cases in our imputed data base. Of these, the variables per cent of infants breastfed at 6 months' and GNP' showed the lowest significance and provided the least contribution to parameter estimates.
Three variables had far larger beta values than any other. These are the per cent of adults who are literate, the prevalence of moderate to severe stunting among under 5-year-olds, and per cent of population with potable water. Very little power was lost by including only these three independent variables rather than the entire variable set. Both are shown. Parameter estimates for the coefficients for the three-variable logistic model were 1.0132 for the intercept, 0.0194 for each unit of adult literacy, 0.0213 for each unit of stunting, and 0.0128 for each unit of population with potable water. The estimated under 5 mortality rate for Iraq in 1996 was 87 per 1000, with a 95% CI of 8095 per 1000 (Table 3).
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Validity Check on Mortality Estimates |
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Data on literacy, population with piped water, and stunting for each governorate from the MICS survey21,22 were grouped by region of the country. Estimates for under 5-year-old mortality rates in the four regions of the country show Baghdad governorate to have the lowest rate. The southern governorates have a 5-year-old mortality rate estimated to be 34% higher than the level in Baghdad. The northern governorates, where United Nations administration and non-governmental organization actions have reduced the impact of the post-Gulf War uprising and displacement of the predominantly Kurdish population, have a rate of mortality higher than Baghdad and lower than the southern governorates (Table 5).
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Implications of Mortality Estimates |
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Endnote |
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In April 1997 the World Food Program, UNICEF, and the Iraqi Ministry of Health carried out a large-scale nutritional survey during a national polio immunization campaign.26,27 The immunization campaign in April included every fifth to tenth child present for immunization. This 1997 Clinic Exit Survey provided a sample of 15 466 children. This over-sampled 12-year-old children relative to those aged 4 and 5. A stratified random sample including 87 of the 850 primary health centres in the country was included. The 15 south and central governorates, covering 85% of the population, were included. The results are similar to those found in the 1996 large-scale multistage cluster sample survey carried out by UNICEF
In March 1998 the World Food Program, UNICEF, and the Iraqi Ministry of Health again carried out a clinic exit interview during the spring polio immunization campaign.28 The results of the 1998 Clinic Exit Survey are similar to the clinic exit interview study in April 1997 and the MICS study of August 1996. Malnutrition is highest in rural areas and slightly higher among males. Results from these studies, taken together, suggest that malnutrition rose rapidly from 1991 to 1996 and has been roughly stable among those under 5 years of age from August 1996 to March 1998.
In February and May 1999 the Government of Iraq and UNICEF in the Centre/South, and UNICEF in the North, carried out a three-stage stratified cluster sample survey of households to assess child and maternal mortality. Within each cluster 15 households were included from the address list created by the 1997 population census. All ever-married women in 21 048 households were interviewed.
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References |
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