David B. Howell
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A. Objectives—students will be able to
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1Ð4. same as Lesson 1.
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5. describe how changing sample size affects variation among several samples.
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B. The experimental question—What percent of the population read “Ebony” in the last week?
C. Issues, and some possible resolutions—
Let’s shoot for the whole student body as our population.
What samples shall we use? (This class. My other classes. Everybody’s English class. Our homerooms. All period One classes.) Some of the samples strike me as more random than others. Let’s discuss those issues.
Let’s take a coin-toss group of classes from a period when all grade levels have classes. We must know two things—how many people in the class and how many read “Ebony” in the last week. We might also want to record what kind of a class and what Grade students are in it so we can analyze our sample for randomness. To get the percent we’ll use Worksheet 1 again.
[When the data is collected, we’ll have Tables something like the foreign car Table I above. The key idea is to compare the range and mean of similar size samples and of groups of different size samples. proceed as follows: for as many samples of 20 25 as possible, calculate the mean. List the lowest and highest values. Calculate the range. Now, using another Worksheet 1, form new samples by combining the original ones into groups of 40-50. Recalculate the Ratio and Percent columns. Repeat the calculations for means, limits, and range.]
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D. Observations and discussion to Objectives—
[In addition to further discussion of the randomness of the samples and of the variations among samples, focus attention on the impact of sample size. If necessary or appropriate, continue to combine samples and to examine the changes in mean (no change!), range, and limits.]