Read this post. It answers all your questions and shows you HOW to do
find your equation of best fit, correlation coefficients, etc.
Before
doing statistics, you have to prepare the calculator by clearing old
data that may generate errors.
A. TO CLEAR OLD DATA
- Press [2nd][+] (MEM) to open the memory management
screen.
- Press [4:ClrAllLists]
- The command echoes on main screen, press [ENTER] to run
it.
- Calculator displays Done.
B. RUN the SETUP EDITOR Command
- Press [STAT][5:SetUpEditor] [ENTER] ; calculator
displays Done.
C. TURN DIAGNOSTICSON option
(optional)
To
obtain the correlation coefficient in a statistical analysis on the
TI8xPlus family of calculators you must activate the DiagnosticsOn
option. To access the command
- You press [2nd] [0] (CATALOG)
- While the list of commands is displayed, press [X^-1]
(D)
- Cursor jumps to first command that starts with D,
dayOfWk(
- Press the DownArrow 9 times to reach DiagnosticsOn
- Select it and press [ENTER]
- Command echoes on main calculator screen with blinking
cursor
- Press [ENTER] to set the option
- Calculator displays Done.
From now on, if a
correlation coefficient has meaning for a regression model, it will be
calculated along with the other statistical results. If it has no
meaning to the model it will not be calculated.
D. ENTER THE DATA Press [STAT][1:Edit]
Type in your D (X ) values in L1
and the N (Y) values in L2 (see picture 1). Sorry the picture does not have YOUR values.
TO OBTAIN THE STATISTICAL RESULTS (optional)
- After you finish entering the data, press [2nd][Quit]
to exit StatEditor.
- Press [STAT] and highlight Menu (CALC)
- In the list select [2:2-Var Stats]
- Command echoes on main screen.
- Press [ENTER] to calculate the stats
Here is
what you get (THESE~ARE NOT YOUR RESULTS). Your results will be different.
Notice
the down arrow next to n=7. That means the results screen has more
values. Press the down arrow to display.
You
notice
that the n=7 line now has an arrow pointing Up. Notice the Down
Arrow on the bottom line (more data is coming). Here is the rest of the
statistical results.
There
is no arrow at the bottom of the picture. End of statistical results.
The
screen
captures with 2-Var Stats summarize all the satistics.
However
there is no correlation coefficient, no line of best fit, etc. To
obtain that you have to perform a regression analysis.
E. PERFORM A REGRESSION ANALYSIS To
perform a regression analysis, you must try several regression models
and then find the one that mimicks the raw data best. In this
particular case, you have already decided to do a linear regression,
and that is good for me. I do not have the time to take you through all
of them. In this step you must select the exponential regression model.
- Press [STAT] , highlight [CALC]
- In the list of regression models select [0:ExpReg]
- The command ExpReg echoes on main calculator
screen.
- If you press [ENTER] you will get you equation but you
will not be able to draw the curve on top of your data to verify the
goodness (no it is not a swear word) of the fit. So you must save the
equation as a function in Y1 variable.
- While ExpReg command is still in command line,
press the [VARS] key.
- Highlight the [Y-VARS] menu and select [1:Function],
then press [ENTER].
- In the Y function variable list select [1:Y1]
- At the command line, you have ExpReg Y1.
- Press [ENTER] to save the equation of best fit in Y1.
Here
are your results. (These are your actual results)
You also have r and its square.
You need to read your theory to know which of the two correlation
coefficients you have been asked to obtain.
Since you saved the
equation in the Y1 function you can draw it. You just have to press
GRAPH and it will be drawn. But that will not tell how good the fit is,
until you see the function drawn on top of the raw data.
DRAWING THE SCATTER PLOT AND BEST FIT CURVE ON SAME SCREEN Regardless
of the curve of best fit, you can draw a scatter plot as follows.
- Press [2nd][Y=] (STATPLOT)
- Select [1:Plot1...Off] and press ENTER to open plot1 configuration
screen
- Use arrow to highlight On and press ENTER
- Use the down arrow to move cursor to the line Type.
- Select the first icon for a scatter plot. NOTE: To
navigate the 6 statistical stat plots on the line Type, use the right
or left arrow (to backtrack), but not the Up or down arrows.
Here
is the configuration screen
Here
plot1
is active (ON), it is scatter plot (first icon) the Xlist is L1
by default but you can change it to some other list. Notice the
highlighted A cursor on XLIST line. It means that the [ALPHA] keyboard
is active.
On the line Mark you can choose the appearnce of the raw
data point.
And here are your two graphs: the raw data scatter
plot and the line of best fit on the same screen. On the picture the ZoomStat option was used.
Now,
it is up to you to accept this model or to try another model.
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