Compare Data Sets

Put up to three data sets next to each other: every summary statistic in one table and the shapes on a shared axis, so differences are obvious at a glance.

12 values

12 values

0 values

On one scale

Class AClass B63.596.5

Box = middle 50% (Q1 to Q3), thick line = median, triangle = mean, dots = individual values.

StatisticClass AClass B
n1212
Mean79.583371.6667
Median79.571.5
Standard deviation (s)9.15984.4381
Min6665
Q17168.5
Q386.574.5
Max9580
IQR15.56
Coefficient of variation11.51%6.19%
Skewness0.0870.288
Outliers (1.5 × IQR)nonenone

Difference in means: 7.9167; in medians: 8. To test whether this is more than sampling noise, run a two-sample t-test.

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A checklist for comparing distributions

Describe centre, spread, shape and unusual features, and use comparative words (“higher”, “more variable”) rather than listing each set separately. For example: “Class A’s median score (82.5) is higher than Class B’s (71.5), and A is more spread out (IQR 15.5 against 6.5); both are roughly symmetric with no outliers.”

For a single data set in depth, use the statistics calculator; for relative spread across scales, the coefficient of variation.

Frequently asked questions

How do you compare two data sets?

Compare centre (mean or median), spread (standard deviation or IQR), shape (symmetric or skewed) and unusual values (outliers). Always plot them on the same scale; numbers alone can hide differences that are obvious in a picture.

Should I compare means or medians?

Use medians and IQRs if either data set is skewed or has outliers; use means and standard deviations if both are roughly symmetric. The table shows both so you can choose.

How do I know if the difference is significant?

Descriptive statistics show how the samples differ, not whether that difference would hold in the wider population. For two groups of numbers, run a t-test (or a Mann–Whitney test for skewed data); for three or more groups, ANOVA. The t-test calculator on this site takes the same data.

How do I compare data sets with different units or scales?

Use the coefficient of variation (SD ÷ mean) to compare relative spread, or convert values to z-scores to compare positions within each set.