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
   1. Bias and sampling error
   2. Bias and sampling error 2
   3. Bias
   4. Measurement bias
   5. Sampling bias
   6. Sampling error
   7. Bias and sampling error - Quiz
   8. Confidence intervals
   9. Confidence intervals - Quiz
   10. Accuracy and precision - theory
   11. 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
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

Sampling bias

(go to Outline)

Sampling bias results from not selecting a truly random sample which is representative of the larger population. For example:

• The chiefs in some villages insisted that the survey team weight and measure their many children. The survey teams did this and included these data in the survey.

• This would probably lead to an underestimate of the prevalence of malnutrition because the chief's children are probably better off than children in general.

• When making lists of households in several villages, the survey team forgot to include households where an ethnic minority lived. People in this minority are routinely discriminated against and cannot, in general, use the villages borehole, but must drink from nearby ponds or streams.

• This would lead to an underestimate of the prevalence of recent diarrhoea as people, especially children, in the ethnic minority are probably more exposed to diarrhoea-causing organisms.