Unit 8: Estimating with Confidence

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Unit 8: Estimating with Confidence Review

Construct and interpret a Confidence Interval Objectives: Construct and interpret a Confidence Interval Explain conditions RIN Critical value Find appropriate sample size for a given CL and ME Emphasize the appearance of “and confidence interval” b\c there is a huge difference between the two parts of this objective. Let students know that the conditions required to use a ConfInt should be familiar.

Example 1 (POD e2 page 516) The Chronicle of Higher Education reports that 72.1% of those college freshmen responding to a survey say that they are attending the school of their first choice. Given that n = 500, estimate the percent of all freshmen who attend their 1st choice with 95% confidence.

Example 2 (POD e2 page 516) In a study involving 18 male postal workers, the sample mean rating of an acceptable lift load was found to be 9.7 kg with a sample standard deviation of 4.3 kg. Suppose that in the population, the distribution of load rating is approx N. Construct and interpret a 99% CI for load rating.

Example 3 A survey from one year ago found that 22% of middle class adults believe that their financial situation has improved. How large a sample would you need to estimate the % who would say the same now to within 3%?

Compute and interpret a 90% CI Example 3 (POD e2 page 506) Time (min) for UA flight from ABQ to Denver on 20 randomly selected days: 57 54 55 51 56 45 53 61 48 52 59 58 50 Follow up Q: if flight is scheduled to depart at 10 a.m., what would you recommend for the published arrival time? Justify your answer. Compute and interpret a 90% CI

Example 4 (POD 2e page 507) Mean time for random sample of 31 bats to consume a frog is 21.9 min with a sample standard deviation of 7.7 min. Find a 95% CI to estimate the average time it takes a bat to consume a frog. (Indian False Vampire Bat consumes both insects and frogs)

Uncertainty is about the interval. What can go wrong? Uncertainty is about the interval. The interval is an est. of plausible values for a param. There is a difference between CL and CI Recognize your variables Give examples of intervals and have students identify the pt. est. and the ME. The blank in bullet 3 is predetermined when we declare how confident we wish to be….