# Scatterplot Worksheet

Use the Scatterplot Worksheet form to create a scatterplot to compare the relationship between two variables.

• What is the nature of the relationship between two variables (the variables are usually a process output Y and a process input X; however, they could also be two process inputs)?
• Is the relationship between the process output Y and a process input X the same for different levels (settings) of a second process input?
When to Use Purpose
Start of project Assists in developing alternatives measurement systems when a variable is difficult or expensive to measure. Highly correlated and logically linked alternative variables can be used as substitute variables.
Mid-project The first rule of data analysis is to graph the data before running any statistical tests. You can use scatterplots along with any statistical tool that tests for relationships between variables (for example, regression).
Mid-project Assess whether an input (X) has a strong relationship with an output (Y) to help eliminate noncritical X's from consideration.
Mid-project Evaluate two inputs to eliminate inputs that duplicate the same information (for example, inputs of Degree Obtained and Years of School are likely to explain the same variation of the output). This case is used primarily in multiple regression with many variables.
End of project If you used this tool earlier as part of the validation of the measurement system, you should reapply it to the improved process to again validate the measurement system.

## Data

Your data must be one or two pairs of numeric variables, which can be continuous or discrete.

## Guidelines

• When you use the Scatterplot Worksheet, you can compare the relationships between two variables (X and Y) at two different levels of a third categorical variable. For example, you can plot yield (Y) versus temperature (X) using two different catalysts. To do this comparison, enter data in the X1 and Y1 columns for the first level of the categorical variable and in the X2 and Y2 columns for the second level of the categorical variable. To compare the relationship between X and Y at more than two levels of a categorical variable, or at levels of more than one categorical variable, use the Graph Your Data analysis capture tool.

## How-to

1. To compare the relationship between two variables, enter a value for X1 and a value for Y1 in Series 1. Add rows to add more values, and optionally, enter label any specific points of interest on the graph. For example, you might want to label outliers.
2. To compare the relationships between two variables at two different levels, enter a value for X2 and a value for Y2 in Series 2. Add rows to add more values, and optionally, label any specific points of interest on the graph. For example, you might want to label outliers.
3. (Optional) Specify X or Y values for reference lines.