1. Warm-up 9.1 Confidence Interval of the Mean

2. Answers to H.W. Discussion Questions

3. 9.1 Confidence Interval for a Mean S.E. for Proportion S.E. for Mean 95% C.I. for a Proportion 95% C.I. for a Mean 97.8 98.0 98.2 98.2 98.2 98.6 98.8 98.8 99.2 99.4 The mean body temperature,,for this sample of ten women is 98.52, and the standard deviation, s, is 0.527. What is the confidence interval for this sample? We don’t have the σ for the population. : (

4. How to find when it is not known. When the assumptions and conditions are met, we can calculate the confidence interval.. The critical value t * n -1 depends on the confidence interval you specify and on the degrees of freedom (n-1), which you get from the sample size.

5. Finding the confidence interval from a list of data 97.8 98.0 98.2 98.2 98.2 98.6 98.8 98.8 99.2 99.4 Finding the confidence interval from the mean and s.d. of a sample Whenever you construct a confidence interval based on t, there are three conditions you must check. Officially, you need a random sample (or random assignment of treatments to units) that i approximately normally or a large enough sample size that the distribution of the sample mean is approximately normal. In the case of a survey, the size of the population should be at least ten times the size of the sample. (Listed in detail on pg 569 of textbook)

6. Problem Residents of a community are concerned of the vehicle speed on a road called Triphammer. One particular day the residents gather the speed of 23 cars. Once the data is gathered, a histogram is created and it appears approximately normal. Describe the conditions. Solve for the confidence interval anyway. Describe the confidence interval in the context and M.E.

7. Common Quiz Mistakes Margin of Error = z* S.E. Form A = +3.5%; Form B = + 14% Step 3 of #2 When drawing the distribution curve, you need to divide the alpha and find the critical value. Form A (alpha = 0.01, 0.005 on both sides with a critical value of + 2.570 Form B (alpha = 0.05, 0.025 on both sides with a critical value of + 1.96 on both sides)