Double Histogram Maker

Class	Freq.	Relative	Cum.	Cum. %
[140, 145)	0	0%	0	0%
[145, 150)	0	0%	0	0%
[150, 155)	0	0%	0	0%
[155, 160)	1	0.5%	1	0.5%
[160, 165)	8	4%	9	4.5%
[165, 170)	38	19%	47	23.5%
[170, 175)	38	19%	85	42.5%
[175, 180)	59	29.5%	144	72%
[180, 185)	44	22%	188	94%
[185, 190)	10	5%	198	99%
[190, 195]	2	1%	200	100%
Total	200	100%

Class

Freq.

Relative

Cum.

Cum. %

[140, 145)

[145, 150)

[150, 155)

[155, 160)

0.5%

[160, 165)

4.5%

[165, 170)

19%

23.5%

[170, 175)

19%

42.5%

[175, 180)

29.5%

144

72%

[180, 185)

22%

188

94%

[185, 190)

198

99%

[190, 195]

200

100%

Total

200

100%

What is a double histogram?

A double histogram (or comparative histogram) plots two data sets, such as the heights of men and women or test scores before and after a course, on the same bins and axes. Because the bins line up, you can compare the two groups bin by bin instead of guessing across two separate charts.

How to make a double histogram

Paste the first group’s values into the first data box and the second group’s into the second.
Rename each data set so the legend reads clearly, for example “Before” and “After”.
In the Bins tab, pick a bin width and choose Overlap, Side by side or Stacked.
If the groups differ in size, switch the y-axis to Percent.
Download the histogram or copy each group’s frequency table.

What to compare

Center: which group has higher typical values? Turn on the mean or median lines in the Design tab.
Spread: is one group more variable? Compare the standard deviations in the Statistics view.
Shape: is one group skewed or bimodal while the other is symmetric?
Overlap: how many values could belong to either group?

Tips for comparing histograms

Always use shared bins. Different bin widths make two histograms impossible to compare; this tool shares them automatically.
Use contrasting colors with about 60% opacity when the bars overlap.
Add the normal curve for each group to compare the overall shapes without the noise of individual bins.

Only have one group? Use the main histogram maker. Want proportions? Try the relative frequency histogram maker.

Frequently asked questions

What is a double histogram?

A double histogram shows the distributions of two data sets on the same axes, using the same bins. It makes it easy to compare where each group is centered, how spread out it is, and how much the two overlap.

Should I overlap the histograms or put them side by side?

Overlapping (semi-transparent) bars are best for seeing how much two distributions overlap. Side-by-side bars make exact heights easier to compare in each bin. Stacked bars show the combined total. Switch between them in the Bins tab.

My two groups have different sizes. How do I compare them fairly?

Switch the y-axis to Relative or Percent in the Bins tab. Each group is then scaled to its own total, so a group of 30 and a group of 300 can be compared directly.

Can I compare more than two data sets?

Yes. Click 'Add data set' to compare up to 6 groups on the same histogram.

How do I make a double histogram from a spreadsheet?

Put each group in its own column with a name in the first row. Click 'Import Excel / CSV', then choose a column for each data set, or click 'Plot every column as its own data set'.

Analyze your data

Your data

Start from an example

What is a double histogram?

How to make a double histogram

What to compare

Tips for comparing histograms

Frequently asked questions

What is a double histogram?

Should I overlap the histograms or put them side by side?

My two groups have different sizes. How do I compare them fairly?

Can I compare more than two data sets?

How do I make a double histogram from a spreadsheet?

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