Standard deviation?????

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Standard deviation?????
Message posted by Candi on September 14, 2000 at 12:00 AM (ET)

I have no idea how to do this, if anyone could explain this in very simple terms, please do.

READERS RESPOND:
(In chronological order. Most recent at the bottom.)

Re: Standard deviation?????
Message posted by JG on September 15, 2000 at 12:00 AM (ET)

When the arithmetic mean is your average
then the standard deviation is your natural measure of variability.
An extremely important distributiion called the normal or bell shaped curve is completely
defined by the mean and standard deviation. The mean is obtained by adding all your numbers and dividing by how many you have. The standard deviation adds the squared deviations from
the mean divides by the number that you have and then takes the square root. When degrees of freedom are taken into account you deviade by n-1 for the standard deviation where n is the number of data points.

Re: Standard deviation?????
Message posted by nancy diehl on September 15, 2000 at 12:00 AM (ET)

To add to the previous response, think of your average (or mean) as a measure where most of the data tends to cluster around.
Think of your standard deviation as the average amount of scatter (or noise) around this mean. To calculate it I find it easier to do
the following. Take your individual data points and calculate these two summary values: 1. sum up all the observations, call this x_sum.
Now square this x_sum. I'll refer to it as (x_sum)sq 2. take each value, square each value, and then sum them up; call this x_sq.
Let n equal the number of values, or observations that you have in your sample. Now do the following: Calculate:

{x_sq - [(x_sum)sq]/n}/(n-1)

This will give you the variance of your sample. Now, take the square root of this result
to get the standard deviation.

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