Distribution
Frequency curve
Shows a smoothed representation of an observed frequency distribution.
- Plot
- Distribution
- Frequency
What it answers
What is the broad shape of the frequency distribution?
- Shape
- Smooth frequency curve
- What it shows
- Approximate modes, skew and spread.
Example
The question
What is the overall shape of basket sizes?
Number of baskets by items per basket (frequency curve)
Illustrative data. It belongs to no company.
When to use it
Use it when
A smooth overview of a sufficiently populated distribution.
Avoid it when
Small samples or a need to preserve exact bin frequencies.
How to read it
Read curve height and peaks under the stated smoothing method.
Note
State smoothing and normalisation.
The data you need
- Layout
- Long table
- Fields
- Value: number
- One row is
- One raw numeric observation. What is the grain?
- Rules
- Use raw observations unless the chosen renderer explicitly accepts summaries or bins. Define missing-value treatment.
- Optional
- Optional frequency Weight. Pre-binned alternative: BinStart,BinEnd,Count; do not treat counts as raw values.
- 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 bin frequencies 3,1,1 at midpoints 12.5,17.5,22.5. Smooth the frequency profile; report that the precise curve depends on the method.
| Value |
|---|
| 10 |
| 12 |
| 12 |
| 18 |
| 23 |