Miscalculation of the Prevalence of Acute Malnutrition in Surveys with Oedematous Children
Since the beginning of the nineties, software has been developed to facilitate the calculation of anthropometric indices and prevalence of malnutrition, i.e. Epi-Info 5 and Epinut 2, developed by the Center for Disease Control. The software has since been updated and currently the most widely used software for the analysis of nutrition surveys is Epi-Info 6, which includes an updated version of Epinut (Dean AG et al).
The system on the Nutrition Information in Crisis Situations (NICS) of the UN Standing Committee on Nutrition has received hundreds of nutrition survey reports from NGOs and UN agencies over the past ten years. However, calculation of the prevalence of acute malnutrition and the classification of children according to the presence of oedema and the weight-for-height index have been incorrect in some of these surveys.
Two hundred and ninety six reports of nutrition surveys conducted by UN and international NGOs between 1993 and 2004 in 17 countries received by NICS have recently been further analysed. The distribution of children surveyed according to their weight-height and presence of oedema was provided in 155 of the 296 survey reports analysed (52.4%). Out of these 155 survey reports, 149 (96.1%) were correctly calculated, i.e. oedematous children were considered severely malnourished and were not included in the distribution of the weight-for-height index (in reference to table 2: a+b+c+d = n), whilst six (3.1%) were incorrectly calculated. Of the 155 survey reports which provide the table of distribution, 30 did not state the software used for the analysis (19%). One hundred and eight surveys (70%) were analysed using Epi-Info 5 and Epinut 2 and 17 surveys (11%) were analysed using Epi-Info 6. The six surveys where the distribution of the children according to their nutrition status was incorrectly calculated had been analysed using Epi-Info 6. This means that of the 17 surveys analysed using Epi-Info 6, 6 (35%) were wrongly analysed, whilst all the surveys analysed with Epi5/Epinut 2 were correctly analysed.
In all the six surveys with miscalculations, oedematous children were counted twice in the table of the distribution of nutrition status: once as oedematous children and once in the distribution of the weight-height index (in reference to table 1: b+c+d = n and a+b+c+d = n+a).
In calculating prevalence of malnutrition, three surveys accounted for oedematous children twice. The other three surveys did not take oedematous children into account as severely malnourished but considered them only according to their weight-height status.
These errors of calculation may be explained by the fact that whilst the older version of Epinut (Epinut 2 used with Epi-Info 5) automatically classifies children with oedema as severely malnourished and excludes them from the analysis of the weight-height index, Epinut in Epi-Info 6 does not. With Epinut in Epi-Info 6 it is necessary to go to an option menu and click a box for the oedematous children to be excluded from the analysis of the weight-for-height index.
Epinut 2 also automatically gives the prevalence and 95% confidence intervals of global and severe acute malnutrition, taking into account oedematous children as severely malnourished. In contrast, with the Epinut version of Epi-Info 6, if there are some oedematous children in the survey, users need to calculate the prevalence of acute malnutrition according to the weight-forheight index and the presence of oedema, and to go through a cumbersome manipulation of creating new variables in order to calculate the 95% confidence intervals.
|Table 1: Classification of children according to the weight-for-height index and oedema|
|Number of children surveyed||Number of oedematous children||Number of children with a weight-forheight <-3 Z-score, excluding oedematous children||Number of children with a weight-forheight >= - 3 Z-score & < - 2 Z-score, excluding oedematous children||Number of children with a weight-forheight >= - 2 Z-score, excluding oedematous children|
|n = a+b+c+d||b||c||d|
Box 1: Calculation of the prevalence of malnutrition
Prevalence of severe acute malnutrition = (a+b)/n
Prevalence of moderate acute malnutrition = c/n
Prevalence of (global) acute malnutrition =(a+b+c)/n
|Table 2: Recalculation of the prevalence of malnutrition|
|Number of children||Number of children with oedema||Proportion of children with oedema < - 2 Z-scores||Prevalence from the survey report||Recalculated prevalence|
aSurveys where oedema were counted twice
bSurveys where oedematous children were not taken into account as severely malnourished children
cThe lower figure is drawn from the hypothesis that all the oedematous children have a weight-height < - 2 Zscores; the upper figure is drawn from the hypothesis that none of the oedematous children have a weightheight index < - 2 Z -scores
dThe lower figure is drawn from the hypothesis that all the oedematous children (in the limitation of the total number of severely malnourished children) have a weight-height < - 3 Z - scores; the upper figure is drawn from the hypothesis that none of the oedematous children have a weight-height index < -3 Z-scores
Based on the sample of survey reports, prevalence of acute malnutrition was recalculated (table 2). For the three surveys where oedematous children had been double-counted, recalculated prevalence was lower than the prevalence given in the reports. The more oedematous children in the survey and the higher the proportion of oedematous children having a weight-height index less than - 2 Zscores, the greater the difference between prevalence of malnutrition calculated in the report and the recalculated prevalence.
For the three surveys where oedematous children were not classified as severely malnourished, the prevalence of severe acute malnutrition was significantly under-estimated in the survey reports.
Verification of the calculation of the prevalence of malnutrition was only possible for half of the 296 surveys which were conducted in 17 countries and made available to NICS over the last ten years. While only 17 of these were analysed using Epi-info 6, it is worrying that about one third of these surveys reported incorrect calculations.
In this study, miscalculations of the prevalence of malnutrition did not lead to results which were substantially different from the actual prevalence. However, the prevalence of severe malnutrition was significantly incorrect in three surveys and the greater the proportion of oedematous children in a survey the greater the miscalculation.
This study highlights the fact that the analysis of nutrition surveys may be challenging and that action is needed to improve the process, such as the dissemination of existing guidelines and the development of training material and of user-friendly software.
Amanual on "data processing and analysis of nutrition surveys using Epi-Info 6" was edited by Save the Children in August 2003 (SC, 2003). Workers involved in the analysis of nutrition surveys are encouraged to use this manual or alternatively, to use the older version of Epi-Info (Epi-Info 5/Epinut 2), although this version is no longer available on the internet.
Epinut in Epi-info 6 should be updated, and any updates of existing software and development of new software to analyse nutrition surveys should be made as userfriendly as possible particularly with regard to accounting for oedematous children as severely malnourished.
Dean AG et al. Epi Info version 6 a word processing database and statistics program for public health. Center for Disease Control and Prevention, Atlanta, GA. Epi-Info Museum, Key events in the development of Epi-Info http://www.cdc.gov/epiinfo/background.htm
SC 2004 Using Epi-info 6.04, data processing and analysis of nutrition surveys, a training manual, Save the Children, London. Sphere 2004 Handbook, Chapter 3: Minimum standards in food security, nutrition and food aid, Geneva. WHO 2000 The management of nutrition in major emergencies. WHO, Geneva.
For further information contact; Claudine Prudhon at firstname.lastname@example.org
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Reference this page
Miscalculation of the Prevalence of Acute Malnutrition in Surveys with Oedematous Children. Field Exchange 24, March 2005. p7. www.ennonline.net/fex/24/miscalculation