R: A Geometric Reliability Index as Suggested by Leggett &...

GRI {qualV} | R Documentation

## A Geometric Reliability Index as Suggested by Leggett \& Williams

### 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.

### 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)

[Package qualV version 0.3-3 Index]