Texas Instruments TI-84 PLUS SILV Guidebook - Page 223

4. Press ... | to display the STAT TESTS menu, and then press † until 8:TInterval is highlighted. 5. Press Í to select 8:TInterval. The inferential stat editor for TInterval is displayed. If Data is not selected for Inpt:, press | Í to select Data. Press † y 9 and press † until HGHT is highlighted and then press Í. Press † † Ë 99 to enter a 99 percent confidence level at the C-Level: prompt. 6. Press † to move the cursor onto Calculate, and then press Í. The confidence interval is calculated, and the TInterval results are displayed on the home screen. Interpreting the results The first line, (159.74,173.94), shows that the 99 percent confidence interval for the population mean is between about 159.74 centimeters and 173.94 centimeters. This is about a 14.2 centimeters spread. The .99 confidence level indicates that in a very large number of samples, we expect 99 percent of the intervals calculated to contain the population mean. The actual mean of the population sampled is 165.1 centimeters, which is in the calculated interval. The second line gives the mean height of the sample v used to compute this interval. The third line gives the sample standard deviation Sx. The bottom line gives the sample size n. To obtain a more precise bound on the population mean m of women's heights, increase the sample size to 90. Use a sample mean v of 163.8 and sample standard deviation Sx of 7.1 calculated from the larger random sample. This time, use the Stats (summary statistics) input option. 1. Press ... | 8 to display the inferential stat editor for TInterval. Press ~ Í to select Inpt:Stats. The editor changes so that you can enter summary statistics as input. Chapter 13: Inferential Statistics and Distributions 216