because of two things- a) both positive and negative deviations mean something about the general variability of the data to the analyst, if you added them they'd cancel out, but squaring them results in positive numbers that add up. b) a few larger deviations are much more significant than the many little ones, and squaring them gives them more weight. Sigma, the square root of the variance, is a good pointer to how far away from the mean you are likely to be if you choose a datum at random. the probability of being such a number of sigmas away is easily looked up.
Equal in Variance
The mean deviation (also called the mean absolute deviation) is the mean of the absolute deviations of a set of data about the data's mean. The standard deviation sigma of a probability distribution is defined as the square root of the variance sigma^2,
Standard deviation = square root of variance.
Square the standard deviation and you will have the variance.
Yes, the variance of a data set is the square of the standard deviation (sigma) of the set. This means that the variance is always a positive number, even though the data might have a negative sigma value.
The variance
the small greek letter sigma squared.
Sigma is a Greek symbol used for many variables in mathematics and science. However, within statistics, the variance is sigma squared and it is always positive. Sigma is used as the standard deviation of a population, and as calculated, it is always equal or greater than 0 (a positive number). However, in discussing errors, one can consider adding or subtracting sigma, ie the error in our experiment is +/- one sigma from the population.
because of two things- a) both positive and negative deviations mean something about the general variability of the data to the analyst, if you added them they'd cancel out, but squaring them results in positive numbers that add up. b) a few larger deviations are much more significant than the many little ones, and squaring them gives them more weight. Sigma, the square root of the variance, is a good pointer to how far away from the mean you are likely to be if you choose a datum at random. the probability of being such a number of sigmas away is easily looked up.
Equal in Variance
Standard deviation is the square root of the variance.
It's a lower-case Greek sigma followed by a superscript 2, in other words, "sigma-squared".
Yes. Please see the related link, below.
Variance cannot be negative.
The mean deviation (also called the mean absolute deviation) is the mean of the absolute deviations of a set of data about the data's mean. The standard deviation sigma of a probability distribution is defined as the square root of the variance sigma^2,
Standard deviation = square root of variance.