Texas Instruments TI-84 PLUS - Graphing Calculator Manual Book page 189

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
23. Press o to display the Y= editor.
Press ' to clear the linear regression
. Press } Í to turn on plot 1.
equation from
Y1
Press ~ Í to turn off plot 2.
24. Press q
to select
9
menu. The window variables are adjusted
automatically, and the original scatter plot of time-
versus-length data (plot 1) is displayed.
25. Press ... ~ ƒ ã
the menu.
STAT CALC
home screen.
Press y d † y e † † t a Í † to
highlight
Calculate
: You can also use the
Note
menu,  ~
FUNCTION
26. Press Í to calculate the power regression.
Values for and
a b
screen. The power regression equation is stored
in . Residuals are calculated and stored
Y1
automatically in the list name
27. Press s. The regression line and the scatter
plot are displayed.
from the
9:ZoomStat
ä to select
A A:PwrReg
is pasted to the
PwrReg
.
VARS Y-VARS
to select .
1 Y1
are displayed on the home
.
RESID
b
.
ZOOM
from
Chapter 12: Statistics 182