# What is a good standard deviation number?

## What is a good standard deviation number?

Statisticians have determined that values no greater than plus or minus 2 **SD** represent measurements that are more closely near the true value than those that fall in the area greater than ± 2SD. Thus, most QC programs call for action should data routinely fall outside of the ±2SD range.

## How do you interpret standard deviation numbers?

More precisely, it is a measure of the average distance between the values of the data in the set and the mean. A low **standard deviation** indicates that the data points tend to be very close to the mean; a high **standard deviation** indicates that the data points are spread out over a large range of values.

## What does a standard deviation of 20 mean?

For the set of test scores, the **standard deviation is the** square root of 75.

## Can you have a standard deviation with 2 numbers?

For any two observed values x1,x**2** the sample **standard deviation** is s=|x**2**−x1|/√**2**.

## Is Mean Deviation greater than standard deviation?

A **standard deviation** close to 0 indicates that the data points tend to be close to the **mean** (shown by the dotted line). The further the data points are from the **mean**, the **greater** the **standard deviation**.

## How do you get the standard deviation?

**To calculate the standard deviation of those numbers:**

- Work out the Mean (the simple average of the numbers)
- Then for each number: subtract the Mean and square the result.
- Then work out the mean of those squared differences.
- Take the square root of that and we are done!

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