Skewness: what it means and how to read it

In the report: skewness — The asymmetry of the distribution, with the sample correction as in Excel and SPSS; empty for fewer than 3 values or a column of equal values.

How to read it

0 — symmetric; positive — a long tail of high values (income); negative — a long tail of low values (an easy test). A rough guide, not a test: within ±1 the data are roughly symmetric; many authors accept |skewness| up to 2 for t-tests and ANOVA (Kline).

In plain words

A teacher gave an easy test to 50 students. Most got 90 or more, but a few got 40, and she wanted to know how lopsided the marks were. She asked for skewness and got minus 1.2. A number below zero means a long tail of low marks, with most students bunched up at the top. The pocket money of the same class would give a number above zero: a few kids with a lot of money make a long tail of high amounts. Zero means even on both sides. As a rough guide, between minus 1 and 1 is only a little lopsided, so her minus 1.2 is a bit more than that.

How it is computed

n / ((n − 1)(n − 2)) · Σ ((x − x̄) / s)³; with pop = TRUE: Σ ((x − x̄) / s)³ / n

Where you see it

STATS_DESCRIPTIVE — Column-wise descriptive statistics with flexible metric selection and optional column filtering.

Kurtosis — Excess kurtosis: how heavy the tails are compared with the normal distribution (0), with the sample correction as in Excel and SPSS; empty for fewer than 4 values or a column of equal values.
First quartile — The first quartile: 25% of the values are below it; computed as in SPSS, so it can differ from the Sheets QUARTILE and PERCENTILE functions.
Third quartile — The third quartile: 75% of the values are below it; computed as in SPSS, so it can differ from the Sheets QUARTILE and PERCENTILE functions.
10th percentile — The 10th percentile: 10% of the values are below it; computed as in SPSS, so it can differ from the Sheets QUARTILE and PERCENTILE functions.
90th percentile — The 90th percentile: 90% of the values are below it; computed as in SPSS, so it can differ from the Sheets QUARTILE and PERCENTILE functions.

Get it in your sheet

One formula in a cell gives the whole report, Skewness included. ALS Stats is a free add-on for Google Sheets™.

Install ALS Stats from Google Workspace Marketplace (opens in a new tab)