The power regression option finds the equation of an equation of the form
y = axb that best fits a set of data. First, enter
the data . Press .
The values of both x and y must be greater than zero. (This is because
the method for determining the values of a and b in the regression equation
is a least-squares fit on the values for ln x and ln y.) Press
to select CALC.
(The power regression option can also be obtained by using the
to select option A and pressing )
then press .
Therefore, the best-fit power equation for this data is approximately
y = 1.13x2.43. The TI-83 calculates the correlation coefficient,
r. In this case, r is about 0.998. The value of r lies between -1 and 1,
inclusive. It is a measure of how well the regression equation fits the
data. A value of -1 or 1 indicates a perfect fit. It also calculates the
value of the coefficient of determination, r2.
The TI-83 stores the regression equation. The equation can be graphed
and is transfered to
without typing the equation as follows. Press
to select EQ.
to view the regression equation and press .
The equation is now entered in .
The data points can also be viewed. Access STAT PLOTS by pressing
to turn the plots on. Press .
Note: The TI-83 calculates the correlation coefficient r and the value of r2,
the coefficient of determination.