Range, absolute deviations and variance

Range=max-min. Mean absolute deviation about the mean is ∑|x-mean|/n. Population variance is σ²=∑(x-μ)²/N; sample variance is s²=∑(x-mean)²/(n-1). Standard deviation is the square root of variance. Variance has squared units; standard deviation has original units. Squared deviations emphasise extreme values. Use the sample divisor when estimating a population variance from an independent random sample.