Performance measures
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Introduction
Here is a selection of measures you can use for assessing the performance of your model.
Nash-Sutcliffe efficiency
The Nash-Sutcliffe efficiency is a widely used performance measure based on the error variance. It is implemented as NSeff() in the topmodel package. It takes two vectors, containing the simulated (Qsim) and observed (Qobs) discharge:
Eff <- NSeff(Qobs,Qsim)
The underlying code is very simple:
NSeff <- function (Qobs, Qsim){ Qsim <- Qsim[!is.na(Qobs)] Qobs <- Qobs[!is.na(Qobs)] Qobs <- Qobs[!is.na(Qsim)] Qsim <- Qsim[!is.na(Qsim)] NS <- 1 - (sum((Qobs - Qsim)^2)/sum((Qobs - mean(Qobs))^2)) return(NS) }
Coefficient of determination
The coefficient of determination is the square of the Pearson's product-moment correlation coefficient. Note that the COD only evaluates linear relations between variables!
COD <- cor(Qobs, Qsim, use="complete.obs")^2
Root mean squared error
As the name suggests, the root mean squared error is the square root of the mean squared error:
RMSE <- (mean((Qobs - Qsim)^2))^0.5