gamlss (version 4.2-8)

Rsq: Generalised (Pseudo) R-squared for GAMLSS models

Description

This function gives the generalised R-squared of Nagelkerke (1991) for a GAMLSS model.

Usage

Rsq(object, type = c("Cox Snell","Cragg Uhler","both"))

Arguments

object

a GAMLSS object

type

which definition of R squared. Can be the "Cox Snell" or the Nagelkerke, "Cragg Uhler" or "both".

Value

• The Rsq() produces a single value if type="Cox Snell" or "Cragg Uhler" and a list if type="both".

Details

The Rsq() function uses the definition for R-squared: $$R^2=1- \left(\frac{L(0)}{L(\hat{\theta})}\right)^(2/n)$$ where $L(0)$ is the null model (only a constant is fitted to all parameters) and $L(\hat{\theta})$ is the current fitted model. This definition sometimes is referred to as the Cox & Snell R-squared. The Nagelkerke /Cragg & Uhler's definition divides the above with $$1- L(0)^(2/n)$$

References

Nagelkerke, N. J. (1991). A note on a general definition of the coefficient of determination. Biometrika, 78(3), 691-692.

Stasinopoulos D. M. Rigby R.A. (2007) Generalized additive models for location scale and shape (GAMLSS) in R. Journal of Statistical Software, Vol. 23, Issue 7, Dec 2007, http://www.jstatsoft.org/v23/i07.

See Also

GAIC

Examples

data(aids)
m1 <- gamlss(y~x+qrt, data=aids, family=NBI)
Rsq(m1)
Rsq(m1, type="both")
rm(m1)