Confidence Interval Estimate for Standard Deviation or Variance Access tech supplements, videos, and data sets at www.TriolaStats.com TECH CENTER continued Confidence Interval 1. Click Stat in the top menu. 2. Select Variance Stats in the dropdown menu, then select One Sample from the submenu. 3. Using Summary Statistics: Select With Summary from the submenu and enter the sample variance and sample size. Using Sample Data: Select With Data from the submenu and select the desired data column(s). 4. Select Confidence interval for S2 and enter the desired confidence level. 5. Click Compute! StatCrunch 1. Download and install the Michael Lloyd programs S2INT and ZZINEWT (available at www.TriolaStats.com) on your TI-83>84 Plus Calculator. 2. Press N, select S2INT from the menu, and press [ twice. 3. Enter the sample variance Sx2, sample size n, and confidence level C-Level. Press [ after each entry. 4. Wait for the sx2 confidence interval to be displayed. (Be patient; it may take a while!). 5. Press [ to view the sx confidence interval. TI-83>84 Plus Calculator 352 CHAPTER 7 Estimating Parameters and Determining Sample Sizes R command not available at time of publication. R is rapidly evolving, and an updated list of statistical commands is available at TriolaStats.com. R Statistical Literacy and Critical Thinking 1.Margin of Error a. Why does “margin of error” have no relevance for confidence interval estimates of s or s 2? b. What is wrong with expressing the confidence interval of 7.6bpm 6 s 6 14.2bpm (from Example 2) as 10.9 bpm { 3.3bpm? 2. Requirements a. What are the requirements for constructing a confidence interval estimate of s or s 2? b. How do the requirements from part (a) differ from the requirements for constructing a confidence interval estimate of m? c. In the California Daily 4 lottery, 4 numbers from 0 to 9 are randomly selected with replacement. Can the methods of this section be used to estimate s for the numbers that are selected in this lottery? Why or why not? 3.Red Blood Cell Count Here is a 95% confidence interval estimate of s obtained by using the red blood cell counts of adult females listed in Data Set 1 “Body Data” in Appendix B: 0.360 1million cells>mL2 6 s 6 0.454 1million cells>mL2. Identify the corresponding confidence interval estimate of s 2 and include the appropriate units. 4.Critical Values A sample consists of 20 weights of McDonald’s French fries. Find the critical values x2 L and x2 R used to construct a 95% confidence interval estimate of s. Finding Critical Values and Confidence Intervals. In Exercises 5–8, use the given information to find the number of degrees of freedom, the critical values X2 L and X2 R, and the confidence interval estimate of S. The samples are from Appendix B and it is reasonable to assume that a simple random sample has been selected from a population with a normal distribution. 5.Nicotine in Menthol Cigarettes 95% confidence; n = 25, s = 0.24 mg. 6.Weights of Dollar Coins 95% confidence; n = 20, s = 0.04111g. 7-3 Basic Skills and Concepts
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