HP 39GS HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 143

Confidence interval: T-Int 1-µ In the previous example we found that the evidence of our sample indicated that the mean number of matches in the boxes was not 50. Suppose we now want to know, at the 95% confidence level, within what range of values the true population mean lies. Change back to the SYMB view and the method of Conf Interval. The type of interval is converted to the equivalent type of T-INT: 1 µ. In the NUM SETUP view use the import facility as before to import the values from our sample data. The default confidence level is 99% so you will need to change that to 0.95. Changing to the NUM view gives the minimum and maximum values for the population mean of 50.16 to 52.44 at a 95% confidence level. As before, a more visual display can be seen in the PLOT view. Thus the sample data indicates in our two examples that: • we can be confident the average number of matches is not 50 with less than a 5% chance of being wrong, and • we can conclude, with a confidence of 95%, that the true average number of matches is between 50.16 and 52.44. 143