Other Sampling Methods

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# Other Sampling Methods - PowerPoint PPT Presentation

Other Sampling Methods. Section 3.1B. Why not SRS?. Sometimes it’s just not feasible or practical. Sometimes there are statistical advantages to using more complex sampling methods. Stratified Random Sample.

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## Other Sampling Methods

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### Other Sampling Methods

Section 3.1B

Why not SRS?
• Sometimes it’s just not feasible or practical.
• Sometimes there are statistical advantages to using more complex sampling methods.
Stratified Random Sample
• Divide the population into groups of individuals that are similar in some way that is important to the response.
• Choose a separate SRS in each stratum
• Combine these to form the full sample
Example

To survey radio station about the most requested songs we randomly choose 100 radio stations from each geographic location.

Cluster Sample
• Divide the population into groups or clusters.
• Randomly choose some of these clusters.
• All individuals in the chosen clusters are the sample
Example of Cluster

Survey AP students to see if they had enough time to take the test. We randomly pick some of the schools that took the test & every student at the selected schools are surveyed.

Activity: Sampling Sunflowers
• Use Table D or technology to take an SRS of 10 grid squares using the rows as strata. Then, repeat using the columns as strata.
Sampling and Surveys
Create a SRS

19223 95034 05756 28713 96409 12531

42544 82853 73676 47150 99400 01927

27754 42648 82425 36290 45467 71709

Create a stratified by Rows

77558 00095 32863 29485 82226 90056

52711 38889 93074 60227 40011 85848

48767 52573 95592 94007 69971 91481

Create a stratified by columns

68417 35013 15529 72765 85089 57067

50211 47487 82739 57890 20807 47511

81676 55300 94383 14893 60940 72024

Create a cluster.

19223 95034 05756 28713 96409 12531

42544 82853 73676 47150 99400 01927

27754 42648 82425 36290 45467 71709

Systematic Sampling

This is where you survey every kth person. You randomize it by randomly choosing where to start.

In a large city school system with 20 elementary schools, the school board is considering the adoption of a new policy that would require elementary students to pass a test in order to be promoted to the next grade. The PTA wants to find out whether parents agree with this plan.
• Tell what type of sampling was used and what biases (if any) might result.
• Don’t forget convenience and voluntary.
Send a survey hoe with every student, and ask parents to fill it out and return it the next day.
Randomly select 20 parents from each elementary school. Send them a survey, and follow up with a phone call if they do not return the survey within a week.
Run a poll on the local TV news, asking people to dial one of two phone numbers to indicate whether they favor or oppose the plan.
Hold a PTA meeting at each of the 20 elementary schools and tally the opinions expressed by those who attend the meetings.
Go through the district’s enrollment records, selecting every 40th parent. PTA volunteers will go to those homes to interview the people chosen.
Example: Sampling at a School Assembly
• Describe how you would use the following sampling methods to select 80 students to complete a survey.
• (a) Simple Random Sample
• (b) Stratified Random Sample
• (c) Cluster Sample
Sampling and Surveys
Homework
• Page 227 (17-25) odd
• Page 230 (37-42)
• Bias Worksheet