Scatter Diagram

Description :

Scatter Diagram Is used to investigate the possible relationship between two variables that both relate to the same "event".

When to Use:

• When you have paired numerical data.

• When trying to identify potential root causes of problems.

• After brainstorming causes and effects using a fishbone diagram, to determine objectively whether a particular cause and effect are related.

• When determining whether two effects that appear to be related both occur with the same cause.

Procedure:

1. Collect pairs of data where a relationship is suspected.

2. Draw a graph with the independent variable on the horizontal axis and the dependent variable on the vertical axis. For each pair of data, put a dot or a symbol where the x-axis value intersects the y-axis value. (If two dots fall together, put them side by side, touching, so that you can see both.)

3. Look at the pattern of points to see if a relationship is obvious. If the data clearly form a line or a curve, you may stop. The variables are correlated. You may wish to use regression or correlation analysis now. Otherwise, complete steps 4 through 7.

4. Divide points on the graph into four quadrants. If there are X points on the graph,

5. Count X/2 points from top to bottom and draw a horizontal line.

6. Count X/2 points from left to right and draw a vertical line.

7. If number of points is odd, draw the line through the middle point.

8. Count the points in each quadrant. Do not count points on a line.

9. Add the diagonally opposite quadrants. Find the smaller sum and the total of points in all quadrants.

10. A = points in upper left + points in lower right

11. B = points in upper right + points in lower left

12. Q = the smaller of A and B

13. N = A + B

14. Look up the limit for N on the trend test table.

15. If Q is less than the limit, the two variables are related.

16. If Q is greater than or equal to the limit, the pattern could have occurred from random chance.