Standard deviation can get quite complex. The good news is we can understand A LOT of its behavior by Calculating Standard Deviation in Simple Cases.

1. The Simplest Case: Only one number in the dataset (or every number is the same).

If there's only one number in the dataset, then it is not "spread out" at all. The standard deviation is $0$. If there are $10$ numbers, but they all equal $5$, then the data is not "spread out" at all. The standard deviation is $0$.

2. The Second Simplest Case: Exactly two numbers inn the dataset.

With two numbers in the dataset, find the standard deviation by following these steps:

Step 1: Calculate the average of the two numbers.

Step 2: Subtract the lower number from the average found in step 1.

That's it, lol. You're done. You could also just find the "positive difference" between the average and the larger number. You get the same answer.

Example

What's the standard deviation of a dataset that includes only the numbers $10$ and $22$?

The average of the two numbers is $16$, so the standard deviation is...

$$\sigma = 16 - 10 = 6$$