growR (version 1.3.0)

willmott: Willmott Index

Description

Willmott's index of model performance as described in Willmott (2012).

Usage

willmott(predicted, observed, ...)

Value

willmott Value between -1 and 1

Arguments

predicted

Vector containing the predictions y.

observed

Vector containing the observations z.

...

Scaling factor c in the denominator in the Willmott index. The originally proposed value of 2 should be fine.

Details

This index takes on values from -1 to 1, where values closer to 1 are generally indicating better model performance. Values close to -1 can either mean that the model predictions differ strongly from the observation, or that the observations show small variance (or both).

References

willmott2012RefinedIndexModelgrowR

See Also

get_bias()

Examples

predicted = c(21.5, 22.2, 19.1)
observed = c(20, 20, 20)
# The Willmott index "fails" in this case, as the variance in the 
# observation is 0.
willmott(predicted, observed)

# Try with more realistic observations
observed = c(20.5, 19.5, 20.0)
willmott(predicted, observed)