Variance

The variance of a random variable is defined as the expected (average) value of the squared difference from the mean. Variance is a measure of the variability of the variable about the mean. The positive square root of the variance is the Standard Deviation.

The range-to-variance ratio measures how well a fitted regression model might predict new values. It's defined as the range of estimated values at the original data points, divided by the average variance of the estimated values. It measures the variation of predicted values due to the model versus the variation due to uncertainty in the model. A high value, greater than 10 for example, indicates that the prediction is likely worthwhile. A low value, less than four for example, suggests that the uncertainty in the model is high enough that predicted changes may not be significant.