Operation Manual

Chapter 12: Statistics 279

Notice the pattern of the residuals: a group of negative residuals, then a group of positive

residuals, and then another group of negative residuals.

The residual pattern indicates a curvature associated with this data set for which the

linear model did not account. The residual plot emphasizes a downward curvature, so a

model that curves down with the data would be more accurate. Perhaps a function such

as square root would fit. Try a power regression to fit a function of the form y = a … x

22. Press o to display the Y= editor.

Press ‘ to clear the linear regression

equation from

Y1. Press }Í to turn on plot 1.

Press ~Í to turn off plot 2.

23. Press q

9 to select 9:ZoomStat from the ZOOM

menu. The window variables are adjusted

automatically, and the original scatter plot of time-

versus-length data (plot 1) is displayed.

24. Press …~ƒã

Aä to select A:PwrReg from

the

STAT CALC menu. PwrReg is pasted to the

home screen.

Press yd¢ye¢. Press ~

1 to

display the

VARS Y-VARS FUNCTION secondary

menu, and then press

1 to select 1:Y1. L1, L2, and

Y1 are pasted to the home screen as arguments to

PwrReg.