Quadratic/Cubic/Quartic Regression
Quadratic Regression fits the second-degree polynomial 
to the data. It displays values for 
. At least three data
points are required. For three data points, the equation is a polynomial fit;
for four or more it is a polynomial regression.
To do a quadratic regression,
we follow the same instructions as for linear regression in Project 6, except
that instead of LinReg (ax+b), we use QuadReg in the STAT CALC
menu.
Instructions for TI-83:
To obtain a quadratic
regression to the data in Project 6:
1. Press: STAT 4 5 (
to select 5: QuadReg from STAT CALC)
2. Press: 2nd 
,
2nd 
,
3. Press: VARS 4 1 (displays VARS Y-VARS FUNCTION)
4. Press: 2 ( selects 2: 
)
Observe that 
, 
, and
are pasted to the home screen as arguments of
QuadReg.
5. Press: ENTER (executes
QuadReg )
Values for ‘a’ ,
‘b’ and ‘c’
are displayed on the home
screen and the quadratic regression equation is stored in 
. To observe the scatter plot and the
regression curve Press:
GRAPH
Cubic Regression fits the third-degree polynomial 
to the data. It displays values for 
At least four data points are required. For
four data points, the equation is a polynomial fit; for five or more it is a
polynomial regression.
To do a cubic regression, we
follow the same instructions as for linear regression in Project 6, except that
instead of LinReg (ax+b), we use CubicReg in the STAT CALC
menu.
Quartic Regression fits the fourth-degree polynomial 
to the data. It displays values for 
At least five data points are required. For
five data points, the equation is a polynomial fit; for six or more it is a
polynomial regression.
To do a quartic regression,
we follow the same instructions as for linear regression in Project 6, except
that instead of LinReg (ax+b), we use QuartReg in the STAT
CALC menu.
Exercise: Write the
quadratic, cubic and quartic polynomial regression to the data in
Project 6(round to two
decimal places).
Quadratic Regression:
Cubic Regression:
Quartic Regression