Boxplot (Box-and-Whisker Plot)

A boxplot (box-and-whisker plot) is a graphical summary of a continuous variable that displays the median, the interquartile range (IQR), the overall range, and potential outliers in a single figure.

How to Read a Boxplot

• The box spans the first quartile (Q1) to the third quartile (Q3); the line inside the box marks the median.
• The whiskers extend to the most extreme values within 1.5 × IQR of the box edges.
• Points beyond the whiskers are flagged as potential outliers (marked with ○, or * for extreme outliers more than 3 × IQR from the box).
• Boxplots also reveal the shape of a distribution: a median off-center within the box, or unequal whiskers, suggests skewness.

Boxplots are especially useful for comparing a variable across groups side by side, and for spotting outliers before running inferential tests.

Creating a Boxplot in SPSS

1. Enter your data in Variable View (define the variable as Scale) and Data View.
2. Go to Graphs → Chart Builder and choose Boxplot, or use Analyze → Descriptive Statistics → Explore and request Factor levels together plots.
3. SPSS marks outliers with ○ (1.5–3 × IQR) and extreme outliers with * (beyond 3 × IQR). Always check flagged cases against the raw data before deciding how to handle them.

For the full SPSS workflow — data entry, descriptive statistics, and academic interpretation — see the SPSS Fundamentals and Boxplot tutorial.

Practice With Your Own Data

Our free Boxplot Calculator builds a boxplot from your own data in seconds, so you can practice reading one before opening SPSS.