Distribution

Mirrored / back-to-back histogram

Compares two distributions on opposite sides of a common numeric axis.

Plot
Distribution
Comparison

What it answers

How do two distributions compare across the same bins?

Shape: Opposing binned bars
What it shows: Differences in distribution shape.

Example

The question

How do the ages of new and long-standing customers differ?

Customers by age band: joined this year and joined before (illustrative)

Back-to-back bars by age band, share of each group. Joined this year: 18-24 22%; 25-34 31%; 35-44 20%; 45-54 13%; 55-64 9%; 65+ 5%. Joined before: 18-24 6%; 25-34 15%; 35-44 22%; 45-54 24%; 55-64 19%; 65+ 14%.

Illustrative data. It belongs to no company.

When to use it

Use it when

Paired populations with shared numeric measurement.

Avoid it when

More than two groups or differing bin boundaries.

How to read it

Compare mirrored bar lengths at each common bin.

Note

Normally two groups and common bin edges.

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.

A long table: one row per observation, few columns. New data adds rows.

Worked example

A10,12,18; B11,23. Mirror counts for bins[10,20),[20,30). A has 3 versus B1 in the first bin.

Group	Value
A	10
A	12
A	18
B	11
B	23

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