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FIGURE 10.4 Run chart

Scatter Diagram

A scatter diagram plots two numerical variables on a chart to determine whether there

is a correlation between them. Scatter diagrams, also known as correlation charts,
display the relationship between these two elements as points on a graph. The closer
these variables are to each other, the closer the variables are related. This relationship
is typically analyzed to prove or disprove cause-and-effect relationships. As an
example, maybe your scatter diagram plots the ability of your employees to perform a
certain task. The length of time (in months) they have performed this task is plotted as
the independent variable on the x-axis, and the accuracy they achieve in performing

this task, which is expressed as a score—the dependent variable—is plotted on the y-
axis. The scatter diagram can help you determine whether cause-and-effect (in this
case, increased experience over time versus accuracy) can be proved. Scatter diagrams
can also help you look for and analyze root causes of problems.

Figure 10.5 shows a sample scatter diagram.

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