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Getting started

Create the folder “ mystat ” (for statistics):

  • Press 2nd VAR-LINK . Press F1 Manage .
  • Press 5:Create Folder . Enter the name “ mystat ” and press Enter twice.

Make mystat your current folder:

  • Press MODE . Arrow down to Current Folder and arrow over and down to mystat .
  • Press Enter twice. You should see the name MYSTAT in the lower left corner.

Creating list names L1 , L2 , and L3 :

  • Press APPS 1:Flashapps . Press Enter .
  • Arrow up into the name area of the lists and over until you reach a blank title area.
  • Press L (above the 4 ). Press alpha . Press 1 . Press Enter .
  • Arrow up into the name area of the lists and over until you reach a blank title area.
  • Press L . Press alpha . Press 2 . Press Enter .
  • Arrow up into the name area of the lists and over until you reach a blank title area.
  • Press L . Press alpha . Press 3 . Press Enter .

Linear regression

Given the data set: (3, 5), (6, 8), (9,7), (5, 20). The xlist is 3, 6, 9, 5 and the ylist is 5, 8, 7, 20. Put the xlist into L1 and the ylist into L2 .

Constructing a scatter plot

  • Make sure you are using Flashapps (Press APPS 1:Flashapps . Press Enter .)
  • SCATTERPLOT: After you are have entered your lists in L1 and L2 , press F2 .
  • Press 1:Plot Setup . Highlight Plot 1 and make sure there are no checks next to any other plots. If there are, arrow to the plot and press F4 .
  • Then arrow back to Plot 1 .
  • Press F1: Define . For Plot Type , press the right arrow and press 1:Scatter .
  • Arrow down, press the right arrow and press 1:Box .
  • Arrow down to x . Press alpha L1 . Arrow down to y and press alpha L2 .
  • Arrow down to Use Freq and Categories? and use the right arrow. Highlight NO and press Enter .
  • Press Enter again.
  • Press F5 Zoomdata . You should see the scatterplot. Press F3 to trace and the arrow keys to see the coordinates of the points.

Calculating the regression equation

  • Press APPS , 1:Flashapps , and Enter .
  • Press F4:Calc .
  • Press 3:Regressions .
  • Press 1:LinReg (ax+b) . For x List , enter alpha L1 . Arrow down. For y List , enter alpha L2 .
  • For Store RegEqn to: , arrow right and arrow down to y1(x) (or any one of the y's) and press Enter .
  • Press Enter . You should see a screen with a , b , r^2 , and r on it. The regression is complete.
  • Write down the equation from the information and press Enter .
  • The linear regression is yhat = 11.2267 - .2133x

Drawing the regression line

  • Press the key with the green diamond on it (it is below the 2nd key) and press Y= (above the F1 key).
  • This is the Line of Best Fit .
  • Press the key with the green diamond on it and press GRAPH (above the F3 key). The line will be drawn.

Outliers

  • When you do Linear Regression, a list called " resid " is created automatically.
  • This list has the “ y – yhat ” values in it.
  • Go into Flashapps and into your lists.
  • Arrow to " resid " so you see it.
  • Then, arrow to the list name L3 . Press F3 .
  • Press 1:names . Arrow down to STATVARS . If it is not checked, press F4 .
  • Then, arrow down to resid . Press Enter . Press ^2 . Press Enter . L3 will have the (y - yhat)^2 values.
  • Press HOME and Press F1 8 to clear it.
  • Press 2nd MATH . Press 3:List . Press 6:Sum . Press alpha (L3) .
  • Depending on how you have MODE Display Digits set, you should see approximately 137.1467. This is the SSE.
  • Calculate s . (You should be HOME .) Press clear .
  • Press the square root symbol and enter 137.1467/2 . (You get the denominator by taking the number of data points and subtracting 2: 4 - 2 = 2 .)
  • Press Enter . You should see 8.2809 (to 4 decimal places).
  • Press the times key and enter 1.9 . Press Enter . You should see 15.7337 .
  • Press clear . Press 2nd VAR-LINK .
  • Arrow down to resid (it is below STAT VARS ). Press Enter . Press Enter again.
  • Arrow up to the list. Scroll through the list using the arrow keys.
  • Compare 15.7337 to the absolute values of the numbers in the list. If any absolute value is greater than or equal to 15.7337, then the corresponding point is an outlier.
  • Absolute values of the numbers in the list are approximately 5.59, 1.95, 2.31, 9.84.
  • None of them are greater than or equal to 15.7337.
  • Therefore, for this data set, no point is an outlier.

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Source:  OpenStax, Collaborative statistics: supplemental course materials. OpenStax CNX. Oct 01, 2008 Download for free at http://legacy.cnx.org/content/col10586/1.2
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