Standard deviation of the group: what it means and how to read it
In the report: Sd — The sample standard deviation of the group (n − 1).
How to read it
How much the values of the group scatter. Very different Sd in the two groups is what Welch's test is for.
In plain words
A coach timed two teams of runners. Both teams ran 400 meters in 70 seconds on average, so he could not tell which team was more even. He looked at the Sd of each team, the standard deviation. Team A came out 1.2 seconds, team B 6 seconds. Now he can say that team A runners usually finished within about a second of 70 seconds, while team B runners were spread from about 64 to 76 seconds. When two groups are this unlike, the test made for unequal groups, Welch's test, is the fair one to use.
Example
The cell with Sd is selected in each report; point at a label to see its note.
- — the sample data (50 rows) the examples use
- —
=STATS_INDEPENDENT(Data!A1:T51, "y,x1", "welch",0.95)
Where you see it
STATS_INDEPENDENT— Independent-samples t-test for two groups: the two selected columns are the groups.
Related values
- N — The number of valid values in the group of the row.
- Mean rank — The average rank of the values of the group; rank 1 is the smallest value of all groups together.
- Sum of ranks — The sum of the ranks of the values of the group.
- Negative ranks — Pairs where the second column is smaller than the first (the difference second − first is negative), as SPSS.
- Positive ranks — Pairs where the second column is larger than the first (the difference second − first is positive).
Get it in your sheet
One formula in a cell gives the whole report, Standard deviation of the group included. ALS Stats is a free add-on for Google Sheets™.
Install ALS Stats from Google Workspace Marketplace (opens in a new tab)