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Unformatted text preview: sample proportion 25 1 n ˆ p 1 n Try It! Louis Harris and Associates Inc. conducted a poll of 1,250 adults to determine How Americans Grade the School System. The first question in the survey was: In general, how would you rate the quality of American public schools? Frequency Distribution of School Quality Responses Excellent 462 Pretty Good 288 Only Fair 225 Poor 225 Not Sure 50 a. What type of response variable is school quality? Categorical (qualitative) b. What graph is appropriate to summarize the distribution of this variable? Bar graph c. What proportion of sampled adults rated the quality of public schools as excellent? ˆ p = (462/1250) = 0.37 or 37% d. What is the conservative 95% margin of error for this survey? n = 1250 so margin of error is 1/1250 = 0.028 or about 2.8% e. Give an approximate 95% (conservative) confidence interval for the population proportion of all adults that rate the quality of public schools as excellent. 0.37 0.028 0.342 to 0.398 or 34.2% to 39.8% Interpretation Note: Does the interval in part (e) of 34.2% to 39.8% actually contain the population proportion of all adults that rate the quality of public schools as excellent? It either does or it doesn’t, but we don’t k...
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