Texas Instruments -84 Plus, Manual Book

Page: 282 / 696

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
b
.
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
… ~ ƒ
ã
A
ä
to select
A:PwrReg
from
the
STAT CALC
menu.
PwrReg
is pasted to the
home screen.
Press
y d ¢ y e ¢
. 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
.