# Question: What Does The Standard Deviation Tell You?

## What is a good value for standard deviation?

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 know if a standard deviation is high or low?

Low standard deviation means data are clustered around the mean, and high standard deviation indicates data are more spread out. A standard deviation close to zero indicates that data points are close to the mean, whereas a high or low standard deviation indicates data points are respectively above or below the mean.

## Why is the standard deviation important?

Standard deviations are important here because the shape of a normal curve is determined by its mean and standard deviation. The mean tells you where the middle, highest part of the curve should go. The standard deviation tells you how skinny or wide the curve will be.

## What does a standard deviation of 1 mean?

A normal distribution with a mean of 0 and a standard deviation of 1 is called a standard normal distribution. Areas of the normal distribution are often represented by tables of the standard normal distribution. … For example, a Z of -2.5 represents a value 2.5 standard deviations below the mean.

## Can a standard deviation be negative?

Standard deviation is the square root of variance, which is the average squared deviation from the mean and as such (average of some squared numbers) it can’t be negative.

## How do you interpret a standard deviation?

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.

## How do you compare mean and standard deviation?

Standard deviation is an important measure of spread or dispersion. It tells us how far, on average the results are from the mean. Therefore if the standard deviation is small, then this tells us that the results are close to the mean, whereas if the standard deviation is large, then the results are more spread out.

## Is it better to have a higher or lower standard deviation?

A high standard deviation shows that the data is widely spread (less reliable) and a low standard deviation shows that the data are clustered closely around the mean (more reliable).

## What number is a low standard deviation?

For an approximate answer, please estimate your coefficient of variation (CV=standard deviation / mean). As a rule of thumb, a CV >= 1 indicates a relatively high variation, while a CV < 1 can be considered low.

## What does a standard deviation of 2 mean?

Specifically, if a set of data is normally (randomly, for our purposes) distributed about its mean, then about 2/3 of the data values will lie within 1 standard deviation of the mean value, and about 95/100 of the data values will lie within 2 standard deviations of the mean value. …

## Where is standard deviation used in real life?

A low standard deviation shows that the answers are very projectable to a larger group of people. A weather reporter is analyzing the high temperature forecasted for a series of dates versus the actual high temperature recorded on each date. A low standard deviation would show a reliable weather forecast.

## What is the relationship between standard deviation and variance?

Key Takeaways. Standard deviation looks at how spread out a group of numbers is from the mean, by looking at the square root of the variance. The variance measures the average degree to which each point differs from the mean—the average of all data points.

## What does it mean if standard deviation is 0?

When you square a real number, the result is always non-negative. … The only way that each squared deviation score can be equal to 0 is if all of the scores equal the mean. Thus, when the standard deviation equals 0, all the scores are identical and equal to the mean.