Given the following data plot the points,
find the "r" value, create a best fit equation and graph it.
x
210
350
460
505
615
650
y
8.2
12.5
14.5
16.3
19.2
20.9
1. Store data in lists:
Put
the x values in L1 and the y values in L2.
To clear the lists first,
Key: STAT Edit
Use the up arrow to highlight the list
name, such as L1.
Press the CLEAR button and press the down
arrow. The list should now be cleared
of any old data. Do the same for L2.
Then, enter your data in L1 and L2 and press2nd QUIT.
2. Use your calculator to plot the data (optional)
Turn on the plot capability to see
given data points displayed:
Key: 2nd STATPLOT 1
ON TYPE(highlight the 1st graph)
Xlist:L1 Ylist:L2
2nd QUIT
To Graph the scatter plot. Key: ZOOM 9 ENTER
3. Find the 'r' value (correlation coefficient)
to see if creating an equation is worth the trouble. (Using
"LinReg(ax+b) in the
STAT menu is simpler than LinRegTTest. )
Key: STAT CALC LinReg(ax+b) L1, L2 ENTER
Determine if 'r' shows a significant linear correlation between x and y to proceed. (For this example r=.996)
[If you have a new TI-83 that you have never used
for this purpose, the r value may be missing.
If
that's the case, you need to perform a one-time operation:
Key 2nd
Catalog; scroll down to DiagnosticON and key ENTER twice. "Done" should
appear on your screen.]
4. Find the best fit (regression) line.
When you found the 'r' value above, you also got the coefficients for the equation. They are 'a' and 'b'. Rounding to 3 decimal places, the equation
for this example is y = .028x + 2.340
5. To graph the line on the screen
with the points, store the equation
in
Y1: and graph it. At Y1, you may
Key in the equation yourself and then
Key: GRAPH or
Key: VARS Statistics EQ RegEQ ENTER
and then Key: Graph or
For the TI-83/84, if you wish to combine steps
4 and 5 above,