Overview
This lecture explains how to create clustered box plots in SPSS using different methods, depending on whether data is separated by category columns or organized with a category variable.
Creating Clustered Box Plots with Category Variable
- Open Graphs > Chart Builder in SPSS to create box plots.
- Choose "Simple Box Plot" and place the measurement variable (e.g., age) on the Y-axis, category variable (e.g., gender) on the X-axis.
- SPSS displays side-by-side box plots for each category (e.g., male and female).
- The "Clustered Box Plot" option groups categories, but you may need to adjust the clustering variable settings to enable the OK button.
Using Box Plot Menu for Separate Variables
- Go to Graphs > Boxplot, select "Simple", then "Summaries of separate variables".
- Add each category (e.g., male, female) as separate variables to display their box plots side by side.
- Note: Box plot scaling may differ depending on whether axis starts at zero or the minimum data value.
Using Analyze > Descriptive Statistics > Explore
- Navigate to Analyze > Descriptive Statistics > Explore for an alternative approach.
- Add the measurement variable to "Dependent List" and the category variable to "Factor List".
- Under "Plots", select only "Boxplot" and deselect other plot types.
- This method outputs both descriptive statistics and box plots by category.
Handling Data in Separate Columns
- If data for each category is in a separate column, use Graphs > Boxplot > Simple > Summaries of separate variables.
- Select both category columns (e.g., male and female) as dependent variables to display box plots.
- For Analyze > Explore, add both category columns to the "Dependent List" for generating box plots.
Key Terms & Definitions
- Clustered Box Plot — A graphical display showing the distribution of a variable across multiple categories side by side.
- Category Variable — A variable indicating the group (e.g., gender) to which each data point belongs.
- Outlier — A data value significantly different from others in the dataset, often marked on box plots.
Action Items / Next Steps
- Practice making clustered box plots in SPSS using both category variable and separate columns.
- Review the differences in axis scaling when interpreting box plots.
- Try Explore and Chart Builder methods to compare outputs.