RMSD (Root Mean Square Deviation)

The root-mean-square deviation (RMSD) is a frequently used measure of the differences between values predicted by a model or an estimator and the values observed. The RMSD represents the square root of the second sample moment of the differences between predicted values and observed values or the quadratic mean of these differences. The RMSD is defined as the square root of the mean squared Deviation. In modeling this is used to measure the geometric difference between observed and modeled data. The RMSD is also known as root mean squared error (RMSE).

where X(Obs,i) is the observation value and X(model,i) is the forecast value.