how do i calculate residual standard deviation 
first you have to calculate the difference between the predicted values and actual values formed around a fitted line this difference is known as the residual value or residuals to calculate the residual standard deviation plug the residuals into the residual standard deviation equation to solve the formula the bottom lineresidual standard deviation is a term used in statistics it describes the difference in standard deviations of observed values vs predicted values as shown by points in a regression analysis regression analysis shows a relationship between two different variables and describes how well you can predict the behavior of one variable from the behavior of another 