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Regression equations and rounding.
Posted:
Nov 5, 1996 11:33 AM


On the TI83, if your machine is set to 2 decimal rounding (under the MODE menu) and you calculate, say, a linear regression line, the coefficients are calculated to the full fourteen digits but only displayed to 2 decimal accuracy. However, if you then store the regression equation into Y1 by choosing it from the menu, it only stores two decimal places. For example, if the machine calculates the equation y=ax+b and determines that a=.1683645274534 and b=245.23785957587 when you then store the regression equation into Y1 you get Y1=.17x+245.24. If you then change the MODE setting to Float but do not recalculate the regression equation and try to store the equation into Y2 you get Y2=.17+245.24. I.E. the machine somehow rounds the equation permanently, even though the coefficients a and b are not.
Strange.
Doug
 Doug Kuhlmann (508)7494242 Phillips Academy dkuhlman@idea.uml.edu Andover, MA 01810



