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
   1. Sampling unit
   2. What is sampling?
   3. Why do sampling?
   4. Goal of sampling
   5. Simple random sampling
   6. Systematic random sampling
   7. Choosing between simple and systematic sampling - Quiz
   8. Cluster sampling
   9. Sampling - Additional resources
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
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

Choosing between simple and systematic sampling - Quiz

(go to Outline)

1

Could you do systematic random sampling in the camp pictured above? a) Yes b) No Correct. The shelters are in neat rows. Incorrect. You certainly could do systematic random sampling. Just calculate the sampling interval, choose a starting random number. Then start counting and sampling at one corner of the camp and continue until you reach the other end of the camp.Your answer has been saved.

You can do systematic random sampling even if households are not numbered. As a result, if you are faced with a large population of unnumbered but systematically organized households, systematic random sampling may be much easier than trying to list and number each household before doing simple random sampling.

2

True or false? In the camp pictured above, there is no list of all the households. Nonetheless, you could easily do systematic random sampling. a) True b) False Correct. It would be very difficult to do systematic random sampling by counting households. Shelters are not arranged in any order, so it would be very difficult to count households while being sure all households were counted once and only once.Incorrect. It would be very difficult to do systematic random sampling. The shelters are not arranged in any order, so it would be very difficult to count down the households while being sure all households were counted once and only once.Your answer has been saved.

So what do you do in the situation pictured above? You have no list of households and the shelters or households are not arranged in an orderly way. This is the real situation in many populations of displaced people.

One thing you could do is pick any eligible child or adult who happens to walk by.

3

True or false? This is a valid method to sample the population to estimate some health outcome. a) True b) False Correct. This is convenience sampling and should never be used in an assessment survey.Incorrect. This is convenience sampling and should never be used in an assessment survey. It is probably not at all representative of the larger population. If you use convenience sampling, you risk making seriously wrong conclusions and misdirecting your program resources based on these invalid conclusions. Your answer has been saved.

4

Which of the following is convenience sampling? (Tick all correct answers.) a) Choosing all the households in which the family names begin with A through E b) Numbering a list of households and selecting them with a random number table c) Selecting the first house at random and then counting down the sampling interval d) Asking anyone who wishes to participate in the survey to come to the health centre on a certain date e) Randomly selecting children who come to the clinic for illness a) Correct. This is convenience sampling. This is not random sampling because a large part of the population, those with names beginning with F-Z, are not eligible to be selected for the sample.a) Incorrect. This is convenience sampling. This is not random sampling because a large part of the population, those with names beginning with F-Z, are not eligible to be selected for the sample.b) Correct. This is random sampling.b) Incorrect. This is random sampling in which each household selected is selected randomly.c) Correct. This is random sampling.c) Incorrect. This is random sampling in which each household selected is selected randomly.d) Correct. This is convenience sampling. Persons in such a sample are "self-selected" meaning that they choose to be selected; they are not randomly selected.d) Incorrect. This is convenience sampling. Persons in the sample are "self-selected" meaning that they choose to be selected; they are not randomly selected.e) Correct. This is convenience sampling. Children coming to the clinic for illness are very different from all children in the population. They are ill, and by definition, have poorer health status than average at the time they come to the clinic. Moreover, their mothers are motivated to seek health care and are therefore may be different from the average mother.e) Incorrect. This is convenience sampling. Children coming to the clinic for illness are very different from all children in the population. They are ill, and by definition, have poorer health status than average at the time they come to the clinic. Moreover, their mothers are motivated to seek health care and are therefore may be different from the average mother.