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# Sampling

sampling

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### Sampling

1. 1. 4(
2. 2. Sampling By Dr. Mona M. Aboserea Professor of Public Health & Preventive Medicine
3. 3. SamplingSampling Non probabilityNon probability ProbabilityProbability Accessibility Quota Simple random Systematic random Stratified Cluster Multistage
4. 4. I- Non probability Sampling (1) Accessibility (convenient) sampling:  The readily accessibly sample units are selected.  They may be : -nearest neighbors or relatives. - volunteers. - hospital cases.  used in: - mass media. - pilot study.
5. 5. Non – probability sample: It does not give a true representation of the population from which it was drawn A- Accessibility sample: It is not representative of the population and generalization of the results can not be set out as we select the accessible sample units. B - Quota sample: - It is improvement of accessibility sample. - It is not representative of the population as it depends on the investigator choice. - The Investigator pick up a sample of a certain size and structure but the choice of the sampling unit does not follow a special scheme but left to his choice. Advantage: It is cheap, quick and does not require sampling frame.
6. 6. Every individual has an equal chance (probability) of being chosen in the sample before the sample is drawn 1-Simple random sample: - Each selected unit has an equal chance of being selected. - Each unit is selected independent of the others. - A sample frame must be present. We can get the number to be selected from tables of random number, tables that are generated by computer depending on the size of the sample. For example if we want to select 5 individuals out of 15 We need first to number all 15 (sampling frame) then randomly we select the needed sample. II- Probability Sampling
7. 7. 2-Systematic random sample: It is a modified method of the simple random sample. The selection depends on a K interval which we get from both the size of the population and the size of the sample. It equals total population / sample size. Its main advantage is that, it does not require a sampling frame. For example k interval can be calculated 15/5 = 3. So we need to take every 3rd person starting from a random number that we select out of the first 3 numbers.
8. 8. In study carried out in the hospital ward, every 10th admitted patient was included in the sample, which sampling procedure is this: • a. Simple random sampling • b. Stratified sampling • c. Quota sampling • d. Cluster sampling • e. Systematic sampling Quiz
9. 9. 3-Stratified random sample: In this type, the population is divided into strata according to some special characteristics for example as sex or age group. From each stratum a random or a systematic selection is used to select those who are going to be included in the study.
10. 10. Males Females
11. 11. Quiz In a village of 300 population, 60% constitute Hindus, 20% Muslims, 10% Jews and 10% Christians. We want to take a sample of 10% of the population to study the eating habits of this population. The best method would be: a. Simple random sampling b. Stratified random sampling c. Systematic random sampling d. Non-random sampling e. Cluster sampling.
12. 12. 4-Cluster sample: A cluster is a group of individuals that is present in certain locality or geographic area. A random or a systematic random of clusters are first selected, and then the selected clusters taken as whole to be included in the study. For example if we need to select 5 villages present in the governorate, then all people living in these villages will be included in the study.
13. 13. 1 2 3
14. 14. 5-Multistage sample:  In a cluster sample if people that are present in the cluster are selected randomly instead of being all taken, this will be called a multistage sampling.  In this situation two-stages for example, the random selection of cluster will be called primary sampling units and the random selected individuals within the cluster will be called secondary sampling units.
15. 15. Thank you
• #### AbdullahAbdullah142

Apr. 21, 2019

sampling

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