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
    1. Introduction
    2. Surveillance - Prospective death reporting
    3. Surveys (retrospective data collection)
    4. Recall period
    5. Determining the length of the recall period
    6. Data collection and the questionnaire
    7. Surveys - Quiz
    8. Surveys measuring mortality - Summary
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

Surveys (retrospective data collection)

(go to Outline)

The second way to measure mortality is by doing a survey. But cross-sectional surveys collect data at a single point in time. How can they measure a rate of something occurring over a period of time?

During a survey, deaths are counted retrospectively by asking survey respondents about deaths which have occurred during a specific period of time.

1

For a crude mortality rate measured during by survey during a specific time period, what is the denominator of the mortality rate? a) The number of survey workers who worked on the survey b) The population of the villages included in the survey c) The total population of the country in which the survey is done d) The number of persons living in households selected for the survey sample Correct. The survey sample of households forms the population and therefore, the total number of persons in households selected for the survey sample forms the denominator of the crude mortality rate. Incorrect. The survey sample of households forms the population and therefore, the total number of persons in households selected for the survey sample forms the denominator of the crude mortality rate. Your answer has been saved.

2

For a crude mortality rate measured during by survey during a specific time period, what is the numerator of the mortality rate? a) The number of survey workers who died during the survey data collection b) The average number of deaths in the villages included in the survey during the past 5 years c) The number of deaths in the country in which the survey is done which occurred in the past year d) The number of deaths reported as having occurred during the specific time period in households selected for the survey sample Correct. The survey sample of households forms the population denominator, and the number of deaths reported in these households is the numerator of the crude mortality rate.Incorrect. The survey sample of households forms the population denominator, and the number of deaths reported in these households is the numerator of the crude mortality rate.Your answer has been saved.

3

Compared to measuring mortality rates with a prospective mortality surveillance system, measuring mortality by doing a survey has what major advantage? The survey data contains both the numerator and denominator of the mortality rate. A prospective surveillance system contains only the numerator of the rate; the denominator must be obtained from another source, such as a census or population estimate.

Of course, mortality rates need a time period in addition to the numerator and denominator. When measuring mortality rates in a survey, the past time period during which deaths are counted is called the recall period. We are interested in learning about only deaths which occurred during the recall period.

However, as mentioned above for prospective death reporting, the estimate of mortality derived from surveys is much less timely than that derived from prospective surveillance. Therefore, it may be much less useful in making timely program decisions. Often, survey mortality estimates are used mainly for advocacy in prolonged or ignored emergencies. Mortality rates may be used to as a measure of the severity of the emergency to get world attention.