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Handout 20 - Sampling Problems

1. Your wing commander wants you as his IG to hold a series of focus groups with wing personnel to find out their perceptions on the wing’s fitness facilities. The total population of the wing is 3600 military and civilian members. The wing’s rank demographics are:

- FGO = 288- GS-10 and above = 72- CGO = 360- Senior NCO (E7-E9) = 360- NCO (E5-E6) = 1008- GS-9 and below = 432- Airmen = 1080

Your wing commander wants to be confident in your findings and ensure there is only a small margin of error. Based on this trust concern, you’ve selected a confidence level of 95% and confidence interval of 5%, using the on-line sample size calculator link, determine your sample size.

Sample Size Calculator Link

Now that you have your sample size, determine how many focus groups you need in each of the rank strata listed above. Your focus groups should be in the 8-10 participants per group range. Show your work by completing the following table.

Rank Strata Number Sub-Population % Sub-population sample Max Participants/group # of Focus Groups

FGO 288 8% 28 10 3

GS-10 and above 72 2% 7 8 1

CGO 360 10% 35 9 4

Senior NCO 360 10% 35 9 4

NCO 1008 28% 97 10 10

GS-9 and below 432 12% 42 9 5

Airmen 1080 30% 104 8 13

Total WG population 3600

Total Sample Size 348 Total Focus groups 40

2. Your wing commander was pleased you developed a sampling strategy that would support the level of confidence requested. However, the time and manpower required to execute all the focus groups isn’t available. Your wing commander asks you if there is another sampling method you could use than would give him some data on what wing members think about wing’s fitness facilities. How would you respond?

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I would suggest cluster sampling.

3. Your WG/CC has designated OJT records as a wing special interest item. Your WG/CC wants to know with confidence that wing OJT records are in compliance with AF guidance. There are 3,000 OJT records in the wing. You do not have the resources to inspect the entire population of records; however, you do have the resources to inspect a sample. Since your WG/CC wants to be confident about the overall state of the wing’s OJT records, you have decided you need to select a sample that is large enough to give you a 95% confidence level with 5% confidence interval. Based on this scenario, answer the following questions.

a. Which broad category of sampling methods should you use?

Probability

b. Which specific sampling method would you use?

Systematic

c. What is your minimum sample size? 341

d. Based on your answer to 3.b., explain the process for selecting your sample.

Essentially systematically number all the OJT records from 1-3000. Starting with one and in multiples of 8.8 rounded to the nearest whole number.

4. Your wing commander wants to know the overall readiness of wing members’ personal mobility bags. The wing commander is also concerned the bags of logistic group personnel (750 members) may be worse than the rest of the wing due to recent morale problems. The inspection team generates a recall of the entire wing (3,000 members) and inspects the bags of the first 100 members that come through the gate. Of those 100 members, 13 were from the logistics group. The results of the bag inspections were:

Wing Overall

85 bags in compliance with personal bag checklist

15 bags not in compliance with personal bag checklist

Logistic Group

5 bags in compliance with personal bag checklist

8 bags not in compliance with personal bag checklist

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The team chief reports to the wing commander that 85% of all wing members’ personal bags are in compliance. He also tells the wing commander that his concern about the logistics group was valid as 62% of all personal bags in the logistics group are not in compliance.

Question: Evaluate the inspection teams sampling methodology and reporting. Explain how you might have done it. Are their conclusions supportable? Explain how you might have approachedthis mission. If using probability sampling, include sample size and sampling methodology. If non-probability, include sampling methodology and how you would evaluate and report the results.

I would have used stratified sampling. Use the exact sampling size for each of the squadron. LRS is about 25% of the wing. With 95% confidence level with 5% confidence interval we come up with a sample size of at least 341. The bag drag sample of 341 is evenly distributed within the units. In this case I would have inspected 85 personnel from LRS. This would have given the wing CC a more accurate accountability of LRS’s readiness.