How do I create side-by-side box plots?

Enable Series Mode in PlotNerd's calculator, then enter each group on a separate line using format 'Group Name: values'. The tool automatically generates side-by-side box plots with color-coded groups.

How many groups can I compare with grouped box plots?

You can effectively compare 2-7 groups. Beyond 10-12 groups, the chart becomes cluttered and harder to read. For many groups, consider using violin plots or ridge plots instead.

How do I interpret overlapping boxes in grouped plots?

Overlapping boxes suggest similar distributions. If the median of one group falls within another group's box (IQR), the groups may not be significantly different. Use notched box plots to test statistical significance visually.

How to Compare Multiple Groups with Side-by-Side Box Plots

Name: PlotNerd
Author: PlotNerd

1. What Are Grouped Box Plots?

A grouped box plot (also called a multi-series box plot or side-by-side box plot) displays multiple box plots on the same chart, allowing you to compare distributions across different groups simultaneously. Instead of creating separate charts for each group, you can see all comparisons at a glance.

Each box plot in a grouped chart represents one data series (e.g., "Class A", "Class B", "Control Group", "Treatment Group"). They share the same Y-axis scale, making it easy to compare medians, quartiles, and outliers across groups.

💡 Key Advantage

Grouped box plots reveal patterns that would be invisible in separate charts: Which group has the highest median? Which has the most variability? Are there outliers in specific groups? All visible in one glance.

2. When to Use Grouped Box Plots

Grouped box plots are ideal for comparing multiple categories or experimental conditions:

✅ Perfect For:

Comparing test scores across multiple classes
A/B testing results (Control vs. Variant A vs. Variant B)
Experimental groups (Placebo vs. Treatment 1 vs. Treatment 2)
Sales performance across different regions
Product metrics across customer segments
Before/after comparisons with multiple time points

⚠️ Consider Alternatives For:

More than 10-12 groups (chart becomes cluttered)
Time series data (use line charts instead)
Very different scales (consider separate charts)
When you need detailed distribution shapes (histograms may be better)

3. Side-by-Side Box Plots: Excel vs. PlotNerd

Many users try to create side-by-side box plots in Excel. While possible, it can be tricky. Here's a quick comparison:

Feature	Excel	PlotNerd
Setup Time	5-10 minutes (requires data formatting)	Seconds (paste & go)
Outlier Detection	Standard (often hidden)	Tukey or MAD (configurable)
Styling	Manual adjustments needed	Auto-styled, professional
Statistical Significance	No built-in visual test	Notched Box Plots supported

In Excel: You typically need to arrange your data in columns, select all columns, go to Insert > Statistic Chart > Box and Whisker. It often requires significant reformatting if your data isn't perfectly structured.

In PlotNerd: Just paste your data (e.g., "Group A: 1, 2, 3") and click Calculate.

4. Step-by-Step: Creating Your First Grouped Box Plot

Creating a grouped box plot with PlotNerd is straightforward. Follow these steps:

Step 1: Enable Series Mode

Click the "Series Mode: Off" button in PlotNerd's calculator to switch to grouped input mode. The button will turn blue and show "Series Mode: On".

Step 2: Enter Your Data

Enter each group on a separate line using the format: Group Name: value1, value2, value3

Example:

Class A: 78, 82, 85, 90, 93, 95
Class B: 70, 75, 80, 82, 88, 91
Class C: 65, 68, 72, 74, 79, 83

Tip: Each group needs at least 4 data points. Use descriptive names (e.g., "Control Group" instead of "Group 1") for clearer charts.

Step 3: Calculate and Visualize

Click "Calculate" to generate your grouped box plot. PlotNerd will:

Calculate quartiles for each group independently
Display all groups side-by-side on the same chart
Use different colors to distinguish groups
Show individual statistics cards for each group

🎯 Try It Now

Ready to create your first grouped box plot? Use the sample data above in PlotNerd's multi-series calculator to see it in action.

Open PlotNerd Calculator

4. Interpreting Grouped Box Plot Results

When comparing multiple groups, focus on these key aspects:

📊 Median Comparison

The median line (the line inside each box) shows the center of each distribution. Compare medians to see which group has higher/lower central tendency.

Example: If Class A's median is at 90 and Class B's is at 80, Class A generally performs better.

📏 Variability Comparison

The box height (IQR) shows variability. Taller boxes = more spread. Compare box heights to see which groups are more consistent.

Example: A narrow box in Class A means scores are tightly clustered, while a wide box in Class B indicates more variation.

🔴 Outlier Detection

Outliers (points beyond whiskers) appear as individual dots. Compare outlier counts and positions across groups.

Example: If only Class C has high outliers, it might indicate exceptional students or data entry errors.

📈 Range Comparison

The whisker length shows the data range. Compare whisker positions to see overall spread differences.

Example: If Class A's whiskers extend from 70 to 100 while Class B's extend from 60 to 95, Class A has a wider overall range.

5. Real-World Examples

Example 1: Classroom Test Scores

Scenario: Compare final exam scores across three math classes.

Data Format:

Period 1: 78, 82, 85, 90, 93, 95, 88, 87
Period 2: 70, 75, 80, 82, 88, 91, 79, 84
Period 3: 65, 68, 72, 74, 79, 83, 71, 76

Insights: Period 1 has the highest median (90) and least variability. Period 3 has the lowest median (74) but similar spread. This suggests Period 1's teaching method may be more effective.

→ Try this example in PlotNerd →

Example 2: A/B Testing Results

Scenario: Compare conversion rates across three website variants.

Data Format:

Control: 2.1, 2.3, 2.0, 2.2, 2.4, 2.1
Variant A: 2.8, 3.0, 2.9, 3.1, 2.7, 3.2
Variant B: 2.5, 2.6, 2.4, 2.7, 2.5, 2.6

Insights: Variant A shows significantly higher conversion rates (median ~2.95%) compared to Control (~2.2%). Variant B performs slightly better than Control but not as well as Variant A.

→ Try this example in PlotNerd →

6. Best Practices and Tips

✅ Do:

Use descriptive group names (e.g., "Treatment Group" not "Group 1")
Limit to 10-12 groups for readability (PlotNerd will warn you if you exceed this)
Ensure each group has at least 4 data points
Use consistent data collection methods across groups
Include sample sizes (n) when reporting results

⚠️ Avoid:

Comparing groups with vastly different sample sizes without noting it
Creating charts with too many groups (becomes cluttered)
Ignoring outliers without investigating their cause
Drawing conclusions without statistical testing (consider notched box plots for significance)

7. FAQ

Q: How many groups can I compare at once?

A: PlotNerd supports any number of groups, but for best visual readability, we recommend ≤10 groups. If you have more than 10 groups, PlotNerd will show a warning suggesting you consider grouping into fewer categories. The chart will still render, but individual box plots may appear narrow.

Q: Can I use different outlier detection methods for grouped plots?

A: Yes! PlotNerd supports both Tukey (1.5×IQR) and MAD methods for outlier detection. You can switch between methods in the results panel, and all groups will use the same method for consistency.

Q: How do I know if differences between groups are statistically significant?

A: For visual significance testing, enable notched box plots in PlotNerd. If the notches (confidence intervals) of two groups don't overlap, their medians are likely significantly different. For formal testing, use statistical tests like ANOVA or Kruskal-Wallis.

Q: Can I export grouped box plots?

A: Yes! PlotNerd supports exporting grouped box plots as PNG or SVG, perfect for presentations and reports. The export includes all groups with their labels and colors preserved.

Q: What if my groups have different sample sizes?

A: Different sample sizes are fine! Each group's statistics are calculated independently. However, be cautious when interpreting results—larger samples tend to have more stable medians. PlotNerd displays the sample size (n) for each group in the results cards.

8. Conclusion

Grouped box plots are powerful tools for comparing multiple data groups simultaneously. Whether you're comparing classroom performance, A/B test results, or experimental conditions, they provide clear visual insights into distribution differences.

With PlotNerd's multi-series box plot creator, you can create professional grouped visualizations in seconds, with support for advanced features like MAD outlier detection and notched box plots for statistical significance testing.

Ready to Create Your First Grouped Box Plot?

Start comparing your data groups today with PlotNerd's free, privacy-focused calculator.

Create Grouped Box Plot Now