## Scatter Diagrams

Scatter diagrams use two variables, one called an independent variable, which is an input, and one called a dependent variable, which is an output. Scatter diagrams display the relationship between these two elements as points on a graph. 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 then 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.

The important point to remember about scatter diagrams is that they plot the dependent and independent variables, and the closer the points resemble a diagonal line, the closer these variables are related. Figure 11.4 shows a sample scatter diagram.

FiGuRE 11.4 Scatter diagram

Score

Time in Months