The use of epidemiological tools in conflict-affected populations: open-access educational resources for policy-makers

Table of Contents

1. Welcome
2. Introduction: Epidemiology in crises
3. Ethical issues in data collection
4. Need for epidemiologic competence
5. Surveys - Introduction
6. Surveys - Description of sampling methods
7. Surveys - Sampling error, bias, accuracy, precision, & sample size
8. Surveys - Resources required for surveys
9. Surveys - Critiquing survey reports
10. Surveillance - When to do surveillance
11. Surveillance - Methods
12. Surveillance - Common problems
13. Programme data
14. Rapid assessment
15. Mortality - Indicators and their measurement
16. Mortality - Data sources
17. Mortality - Interpretation and action
18. Nutrition - Introduction and background
19. Nutrition - Indicators and their measurement
    1. Introduction to anthropometry
    2. Anthropometric indices
    3. Reference populations
    4. Calculation of percent of median
    5. Oedema
    6. Calculation of z-scores
    7. Adults and body mass index (BMI)
    8. Micronutrients - Clinical indicators
    9. Micronutrients - Biochemical indicators
    10. Calculating prevalence
20. Nutrition - Data sources
21. Nutrition - Interpretation and action
22. Health services
23. Vaccination programmes
24. Water supply, sanitation, and shelter
25. Violence
26. Presentation of results
27. Formulating conclusions and recommendations
28. Dissemination and action

Calculation of percent of median

(go to Outline)

There are two common ways of expressing the distance between an individual child who is weighed and measured and the average comparable child in a reference population. The first is percent of median. This is merely the weight of the individual child relative to the average weight of the comparable children in the reference population, expressed as a percentage. This can be calculated from a table giving information about the reference population.

For example, let's return to our 80 cm tall girl who weights 8.0 kg. Below is part of the table for weight-for-height in girls 24-59 months of age. The first column gives the height. The second column gives the average weight for all girls whose weight is equal to the value given in the first column The row highlighted in yellow gives the data for 80 cm tall girls. The average weight for 80 cm tall girls is 10.2 kg. Therefore, the percent of median for our 8.0 kg girl is 8.0 as a percent of 10.2, or:

Absence of acute protein-energy malnutrition, or normal nutritional status, is defined as having a percent of median weight-for-height of 80% or greater. Moderate acute protein-energy malnutrition is defined as having a percent of median weight-for-height of 70-79%. Severe acute protein-energy malnutrition is defined as having a weight-for-height percent of median of less than 70%.

Our individual girl therefore has moderate acute protein-energy malnutrition, as defined by weight-for-height percent of median.

Of course, weight-for-height is not useful if a child has oedema. All children with bilateral oedema are automatically defined as having severe acute protein-energy malnutrition regardless of their weight-for-height percent of median.