GRI {qualV}

Geometric Reliability Index as Suggested by Leggett and Williams (1981)

Description

Given a set of predictions and a corresponding set of observations, the geometric validation index is a reliability index for the predictions.

Usage

GRI(o, p)

Arguments

o

vector of observed values

p

vector of corresponding predicted values

Details

One possible interpretation of 'GRI' is that the simulation is accurate within a multiplicative factor 'GRI', i.e. the observed values fall between 1/GRI and GRI times of the corresponding predicted values. Values close to one indicate a good match.

Value

GRI

geometric reliability index

References

Leggett, L. R. and Williams, L. R. (1981) A reliability index for models. Ecological Modelling, 13, 303-312. doi:10.1016/0304-3800(81)90034-X

See Also

MAE, MSE, MAPE, EF

Examples

# a constructed example
x <- seq(0, 2*pi, 0.1)
y <- 5 + sin(x)             # a process
o <- y + rnorm(x, sd = 0.2) # observation with random error
p <- y + 0.1                # simulation with systematic bias

plot(x, o); lines(x, p)
GRI(o, p)

# observed and measured data with non-matching time intervals
data(phyto)
obsb <- na.omit(obs[match(sim$t, obs$t), ])
simb <- sim[na.omit(match(obs$t, sim$t)), ]
GRI(obsb$y, simb$y)