Distribution
Overlaid histograms
Compares group distributions using histograms on common axes.
- Plot
- Distribution
- Comparison
What it answers
How do group distributions differ?
- Shape
- Overlapping transparent binned bars
- What it shows
- Differences in spread, location and shape.
Example
The question
Do weekend orders take longer to pack than weekday orders?
Minutes to pack an order, weekdays and weekends (illustrative)
Illustrative data. It belongs to no company.
When to use it
Use it when
Comparing a small number of numeric distributions.
Avoid it when
Opaque overlapping bars or incompatible binning.
How to read it
Compare groups within shared bins and use the legend to separate overlaps.
Note
Use common bins and state count versus density.
The data you need
- Layout
- Long table
- Fields
- Group: text; Value: number
- One row is
- One raw observation belonging to a group. What is the grain?
- Rules
- Retain individual observations and group labels. State weighting and missing-data rules.
- Optional
- For box plots only, some tools accept Group,Q1,Median,Q3,WhiskerLow,WhiskerHigh plus separate outliers. Other distributions usually need raw data.
- Preparation
- Keep raw numeric observations, group them if needed and handle missingness explicitly. Choose bins, bandwidth or summary conventions as appropriate to this specific plot.
- Units
- The measurement axis retains its original unit. Frequency uses observations; normalised frequency divides by group sample size; density also depends on interval width.
Worked example
A10,12,18; B11,23. With bins[10,20),[20,30), counts are A3,0 and B1,1; show unequal sample sizes.
| Group | Value |
|---|---|
| A | 10 |
| A | 12 |
| A | 18 |
| B | 11 |
| B | 23 |