Scatterplot Worksheet

Summary

Provides a graphical means for assessing and communicating the relationship between two variables.

Answers the questions:
  • 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

One or two pairs of numeric variables (can be continuous or discrete).

How-To

  1. Enter two values and an optional label for each point to be graphed.
  2. To compare another set of values, enter two more values and an optional label for each point to be graphed.
  3. If you want, specify X or Y values for reference lines.

Guidelines

  • Using the scatterplot form, 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 Scatterplot analysis capture form. This form uses Minitab's Scatterplot command, which allows up to three categorical variables with more levels for each.
  • The label appears in a tooltip when you hold the cursor over the symbol.
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