GRI {qualV} | R Documentation |
Given a set of predictions and a corresponding set of observations, the geometric validation index is a reliability index for the predictions.
GRI(o, p)
o |
vector of observed values |
p |
vector of corresponding predicted values |
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.
GRI |
geometric reliability index |
Leggett, L. R. and Williams, L. R. (1981) A reliability index for models. Ecological Modelling, 13, 303-312.
# 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)