T_interval

# T_interval - Using your TI-83/84 Calculator Estimating a...

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Using your TI-83/84 Calculator: Estimating a Population Mean ( σ Unknown) Dr. Laura Schultz When the population standard deviation ( σ ) is not known (as is generally the case), a confidence interval estimate for a population mean ( μ ) is constructed using a critical value from the Student’s t distribution. The TInterval calculator function will generate this confidence interval using either raw sample data or summary statistics. Remember to confirm that the population is normally distributed and/or n 30 before proceeding to generate any confidence intervals. Generating a t interval from summary statistics: 1. Press S and > to scroll right to select the TESTS menu option. 2. Scroll down to 8:TInterval and press e . 3. To work with summary statistics, highlight STATS and press e . 4. Consider the following example. A introductory statistics class counted how many chocolate chips were in each of 42 bags of Chips Ahoy! cookies. They found ¯ x = 1261 . 57 and s = 117 . 58 chocolate chips per bag. First, note that it is safe to apply the Central Limit Theorem because n 30. Let’s use the given summary statistics to find a 95% confidence interval estimate of the mean ( μ ) number of chocolate chips in all bags of Chips Ahoy! cookies. At the prompts, enter the sample mean ( ¯ x ), sample standard deviation ( s x ), and the sample size ( n ). Enter 0.95 at the C-Level prompt, then highlight Calculate and press e . 5. Your calculator will give you the output screen shown to the right. The confidence interval is being reported in the form ( ¯ x - E , ¯ x + E ), which in this case is (1224.9,1298.2) . Because we are working with summary statistics, we would ordinarily round to the same number of decimal places as originally given for ¯ x . In this case, your calculator rounds the confidence limits even further. That’s okay;

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T_interval - Using your TI-83/84 Calculator Estimating a...

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