|
Scatter
Diagram
The
Scatter Diagram
is a tool for determining the potential correlation between two
different sets of variables, i.e., how one variable changes with the
other variable. This diagram simply plots pairs of corresponding
data from two variables, which are usually two variables in a process
being studied. The scatter diagram does not determine the exact
relationship between the two variables, but it does indicate whether
they are correlated or not. It, by itself, also does not predict
cause and effect relationships between these variables.
The scatter diagram is used to: 1) quickly confirm a hypothesis that two
variables are correlated; 2) provide a graphical representation of
the strength of the relationship between two variables; and 3) serve as
a follow-up step to a cause-effect analysis to establish whether a
change in an identified cause can indeed produce a change in its
identified effect.
To make a scatter diagram
for two variables requiring confirmation of correlation, the following
simple steps are usually followed:
1) collect 50-100 pairs of data for the two
variables and tabulate them;
2) draw the x- and y-axes of the diagram, along with
the scales that increase to the right for the x-axis and upward for the
y-axis;
3) assign the
data for one variable to the x-axis (the independent variable) and the
data for the other variable to the y-axis (the independent variable);
4) plot the data pairs on the scatter diagram, encircling (as
many times as necessary) all data points that are repeated.
Interpretation of the resulting scatter diagram is as simple as looking
at the pattern formed by the points. If the data points plotted
on the scatter diagram are all over the place with no discernible
pattern whatsoever, then there is
no correlation
at all between the two variables of the scatter diagram. An
example of a scatter diagram that shows no correlation is shown in
Figure 1.
Figure 1.
A Scatter Diagram showing no correlation
There is
positive correlation
between two sets of data if an increase in the x-value results in an
increase in the y-value. Figure 2a shows a scatter diagram that exhibits positive correlation. Note that in such a correlation, the data points constitute a perceivable diagonal line that
goes from the lower left to the upper right corner.
<Proceed to Page 2>
See Also:
Matrix Diagram; Ishikawa Diagram
HOME
Copyright
©
2004-2005
SiliconFarEast.com.
All Rights Reserved. |
