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Sampling Methods

Sampling Methods. Several techniques can be used to select a sample from a population. Random Numbers. A random number is chosen in such a way that each number has an equal chance of being chosen. For example writing numbers 1-20 on paper and drawing them from a hat.

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Sampling Methods

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  1. Sampling Methods Several techniques can be used to select a sample from a population.

  2. Random Numbers A random number is chosen in such a way that each number has an equal chance of being chosen. For example writing numbers 1-20 on paper and drawing them from a hat. Or using a random number table. See M4Q textbook page 68-69.

  3. Random Numbers These days computers can quickly generate lists of random numbers On your calculator: MATH ˅ ˅(C PROB)  > ˅ (2 rndInt()  (enter the lower limit)  ,  (enter the upper limit)  )  ENTER

  4. Random Samples In a random sample, each member of the population has an equal chance of being selected. Usually numbers are assigned to each member of the population and then random numbers are selected.

  5. Random Samples Example: Discuss how a random group of 10 students could be chosen from a class of 30

  6. Random Samples Example: See M4Q textbook page 72 example 3.11

  7. Capture-Recapture Sampling Useful for estimating populations that are difficult or impossible to count such as plants or animals

  8. Capture-Recapture Sampling A sample of species are captured, tagged and released. Later another sample is captured and the number of tagged specimens observed. From this the population can be estimated.

  9. Capture-Recapture Sampling Eg: In estimating the number of fish in a lake, 500 fish are caught, tagged and then released back into the dam. A week later a batch of 80 fish are caught and 25 of them are tagged. Estimate the number of fish in the dam.

  10. Capture-Recapture Sampling Fraction of fish tagged in the lake= Number of tagged fish in population Population of fish Fraction of fish tagged in sample= Number tagged in sample Size of sample

  11. Stratified Random Sampling This is when a sample is selected from a population consisting of strata or levels in the sample occurring in the same proportions as they do in the population.

  12. Stratified Random Sampling Example: The number of students in a school is shown. A student council is to be formed consisting of 20 members of the school population. The composition of the council must reflect the proportions in the population. How many from each year level should be selected?

  13. Stratified Random Sampling

  14. Systematic Sampling In systematic sampling, every member of the population is assigned a number, the first person is selected randomly and then we select numbers at regular intervals. The intervals depend on the size of the sample we want.

  15. Systematic Sampling Example: For a population of 240 items, at what intervals should we select items to obtain a sample of • 20 • 40 • 65

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