Distribution
Overlaid density plots
Compares group distribution shapes using estimated density curves.
- Plot
- Distribution
- Comparison
What it answers
How do group density shapes compare?
- Shape
- Several density curves
- What it shows
- Location, spread and tail differences.
Example
The question
How do response times differ between our three support channels?
Response time density by channel (illustrative)
Illustrative data. It belongs to no company.
When to use it
Use it when
Comparing several distributions after normalisation.
Avoid it when
When group sample sizes are the main message.
How to read it
Compare curve locations and widths on the same numeric scale.
Note
Normalised densities do not show relative group sizes.
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
Example A10,12,18; B11,23. Estimate densities on one scale. Each curve has total area 1, so it does not show that A has more observations.
| Group | Value |
|---|---|
| A | 10 |
| A | 12 |
| A | 18 |
| B | 11 |
| B | 23 |