Instructions for finding and using linear regressions on the TI-83 Graphing Calculator
Data: (7.2, 65.5), (6.8, 60), (8, 75), (8.3, 76) and (7.5, 68)
Turn on STAT PLOT:
2nd Y =
Turn on Plot 1, ENTER, highlight On, ENTER
Down arrow, select the first graph,
Down arrow, to select L1,
Down arrow, to select L2,
Down arrow and select the box.
To enter the data:
STAT, 1Edit, ENTER
To clear your lists:
In the L1 column use the up arrow and highlight L1
Clear (nothing will happen)
Down arrow (the list should clear).
In the L2 column do the same thing to clear your list.
In the L1 list each wrist circumference.
7.2 ENTER
6.8 ENTER
8 ENTER
8.3 ENTER
7.5 ENTER
Go back up to the first position at the top of L1
Right Arrow Key
In the L2 list heights
65.5 ENTER
60 ENTER
75 ENTER
76 ENTER
68 ENTER
Set the window:
WINDOW,
Set your Xmin to be smaller than the smallest wrist size. 5 ENTER
Set your Xmax to be larger than the largest wrist size. 10 ENTER
Set Xscl = 1
Set your Ymin to be smaller than the smallest height size. 48 ENTER
Set your Ymax to be larger than the largest height size. 85 ENTER
Set Yscl = 1
Set Xres = 1
Compute the statistics:
STAT, right arrow to CALC, 4LinReg (ax+b), ENTER, ENTER
At this point you will have the following screen:
LinReg
y=ax+b
a=11.00550964
b=-14.30165289
r2=.981406496
r=.9906596267
To write the equation for the linear regression use the numbers in the formula y=ax+b to get y = 11.00550964X+ -14.30165289
The correlation is r = .9906596267. The closer the number is to 1 the better the positive correlation and the closer to -1 the better the negative correlation. If r is close to zero there is no correlation.
Have the calculator graph the linear regression line on the graph. Start from the screen above then go to:
Y= VARS, 5Statistics, ENTER, Right arrow to EQ, 1RegEq, ENTER
At this point the equation should appear in on the Y= screen.
GRAPH
The line should appear on the graph screen.
Use the line to predict the height if given the wrist circumference.
Suppose you want to know how tall a person might be if she has a wrist measure of 7 inches.
2nd , TRACE, 1value, ENTER
At the bottom left side of your screen will appear X=
Press 7 and it will appear on the right of X=, ENTER
This will result in Y=62.736915Öwhich represents how tall persons might be, if they had a wrist size of 7 inches with the given data.
To find the coordinate of a particular point on the graph press TRACE and use the left and right arrow keys to highlight particular points. The x and y values will appear at the bottom of the screen. To toggle from the points to the line use the up or down arrow keys.