More Advanced Scatter Plots
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Ever wonder what you should do if you aren't sure if your scatter plot is truly representative of an increasing or decreasing line?
(without the use of a graphing calculator) 

To study your Scatter Plot in a bit more depth, try the following:

1.  Plot the points in a first quadrant graph as you would do for a normal scatter plot.     

Now, divide your first quadrant grid according to the following rules:

2.  Draw a vertical line so that 1/2 of the points are to the left and 1/2 of the points are to the right of this line.  Count the points to be sure of your placement of the line.  If you have an odd number of points, the "extra point" can go on either side of the line.

3.  Draw a horizontal line so that 1/2 of the points are above and 1/2 of the points are below this line.  Count the points to be sure of your placement of the line.  Again, if you have an odd number of points, the "extra point" can go on either side of the line.

4.  Number these new quadrants I, II, III, IV - starting upper right and moving counterclockwise.

Now, use the following rules to determine your correlation:

5.  Count the number of points in each quadrant. 

6.  Add together the points in quadrants I and III.

7.  Add together the points in quadrants II and IV.

 

 If the sum of I and III is more than twice the sum of II and IV, there is a positive correlation.

If the sum of II and IV is more than twice the sum of I and III, there is a negative correlation.

If neither condition is true, no evidence of correlation exists.

Correlation relationships from CORD Math.