View Full Version : Variance

04-11-2005, 10:25 AM
This post might not belong here, but this seems like the closest thing. Could someone please explain to me what is variance. I understand some basic statistics and basic calculus (although its been awhile) if that helps explain.

04-11-2005, 11:04 AM
variance- The square of the standard deviation.

04-11-2005, 12:31 PM
True, variance = st.dev.^2. And -- it is what it sounds like. It's a measurement of the distribtuion about a mean. To calculate it, you would take the set of points within your sample and the mean. Each point in the sample is subtracted from the mean then squared. These squared differences are then summed. I think that you then take this sum and divide by the sample size. (Maybe it's the square of the sample size or maybe it's the square root of the sample size. I cannot remember exactly.) This number is the variance. The square root of this number is the standard deviation. Both of these numbers are useful in telling you what, exactly, the normal distribution (bell curve) that you are working with would look like exactly. For example, it could be pointy -- that is, high and bulging around the mean which then taper fast as you move outwards -- or fat and rounded like an old volcano. This mathematical exercise, then, lets you know how much "variance" you can expect from the mean. Thus, once you have done the math for a sample, you can use the numbers you calculate to estimate future outcomes for your distribution as an estimate of the population.