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Cluster Sampling

Cluster Sampling. The basics. What are we trying to achieve in a survey?. A sample that is representative of the larger population. EPI Method. Samples groups of person rather than individuals 30 Clusters with 7 persons per cluster = 210 persons

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Cluster Sampling

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  1. Cluster Sampling The basics

  2. What are we trying to achieve in a survey? • A sample that is representative of the larger population

  3. EPI Method • Samples groups of person rather than individuals • 30 Clusters with 7 persons per cluster = 210 persons • Based on smallpox immunization surveys in West Africa in ‘68 and ’69 • Is this as precise as a simple random sample (SRS)?

  4. Design Effect • Cluster sampling is commonly used, rather than simple random sampling, mainly as a means of saving • money when, for example, the population is spread out, and the researcher cannot sample from • everywhere. However, “respondents in the same cluster are likely to be somewhat similar to one • another” . As a result, in a clustered sample “Selecting an additional member from the same cluster • adds less new information than would a completely independent selection”. Thus, for example, in • single stage cluster samples, the sample is not as varied as it would be in a random sample, so that the • effective sample size is reduced. The loss of effectiveness by the use of cluster sampling, instead of • simple random sampling, is the design effect. The design effect is basically the ratio of the actual • variance, under the sampling method actually used, to the variance computed under the assumption of • simple random sampling

  5. Comparison of 2 cluster sample designs • Some problems with EPI cluster sampling • Communities selected by PPS with inaccurate data • Households not selected from a sampling frame (selection bias) • Possibility of non-response bias

  6. Compact cluster sampling • Still select clusters based on PPS from census data • Clusters then divided into segments with equal number of households (HHs) • One segment randomly chosen and all HHs in that segment surveyed • Partially addresses selection and non-response bias

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