evidence {qpcR}R Documentation

Evidence ratio for model comparison with AIC or AICc

Description

The evidence ratio

frac{1}{exp(-0.5 * (AIC2 - AIC1))}

is calculated for fitted models either from two 'drc' objects or two numerical values. Models can be compared that are not nested and where the f-test on residual-sum-of-squares is not applicable.

Usage

  evidence(x, y, type = c("AICc", "AIC"))

Arguments

x a 'drc' object or numerical value.
y a 'drc' object or numerical value.
type Bias-corrected (AICc, default) or original (AIC) versions of the Akaike Information Criterion.

Details

Small differences in AIC values can mean substantial more 'likelihood' of one model over the other. For example, a model with AIC = -130 is nearly 150 times more likely than a model with AIC = -120. Unfortunately, not yet a generic function, so works only with 'drc' objects.

Value

A value of the first model x being more likely than the second model y. If large, first model is better. If small, second model is better.

Author(s)

Andrej-Nikolai Spiess

Examples

### compare two models, four-parameter and five-parameter
m1 <- pcrfit(reps, 1, 2, l4())
m2 <- pcrfit(reps, 1, 2, l5())
evidence(m2, m1)
### ratio of two AIC's
evidence(-120, -123)

[Package qpcR version 1.1-8 Index]