Solution 12067: Population Standard Deviation on the TI-89 Family, TI-92 Family, and Voyage™ 200 Graphing Calculators.
Why is the standard deviation not correct in the dialog box shown on the TI-89 family, TI-92 family, and Voyage 200 graphing calculators?The TI-89 family, TI-92 family, and Voyage 200 graphing calculators calculate two types of standard deviation: sample standard deviation (displayed in the dialog box) and population standard deviation. The population standard deviation, denoted by sx, divides the calculated values by n. The sample standard deviation, denoted by Sx, uses the value n-1 as the denominator.
The TI-89 family, TI-92 family, and Voyage 200 graphing calculators use the sample standard deviation Sx when calculating the variance (Sx2).
Once the statistical analysis has been performed, to find the population standard deviation, input sx on the home screen. To access this variable, press [2nd] [CHAR]  [G] [X]. You would square this value for population variance.
Please see the TI-89 family, TI-92 family and Voyage 200 guidebooks for additional information.