gamlss (version 4.2-4)

centiles.split: Plots centile curves split by x for a GAMLSS object

Description

This function plots centiles curves for separate ranges of the unique explanatory variable x. It is similar to the centiles function but the range of x is split at a user defined values xcut.point into r separate ranges. The functions also tabulates the sample percentages below each centile curve for each of the r ranges of x (for comparison with the model percentage given by cent) The model should have only one explanatory variable.

Usage

centiles.split(obj, xvar = NULL, xcut.points = NULL, n.inter = 4, 
               cent = c(0.4, 2, 10, 25, 50, 75, 90, 98, 99.6), 
               legend = FALSE, main = NULL, main.gsub = "@", 
               ylab = "y", xlab = "x", ylim = NULL, overlap = 0, 
               save = TRUE, plot = TRUE, ...)

Arguments

obj

a fitted gamlss object from fitting a gamlss continuous distribution

xvar

the unique explanatory variable

xcut.points

the x-axis cut off points e.g. c(20,30). If xcut.points=NULL then the n.inter argument is activated

n.inter

if xcut.points=NULL this argument gives the number of intervals in which the x-variable will be splited, with default 4

cent

a vector with elements the % centile values for which the centile curves are to be evaluated

legend

whether a legend is required in the plots or not, the default is legent=FALSE

main

the main title as character. If NULL the default title (shown the intervals) is shown

main.gsub

if the main.gsub (with default "@") appears in the main title then it is substituted with the default title.

ylab

the y-variable label

xlab

the x-variable label

ylim

the range of the y-variable axis

overlap

how much overlapping in the xvar intervals. Default value is overlap=0 for non overlapping intervals

save

whether to save the sample percentages or not with default equal to TRUE. In this case the functions produce a matrix giving the sample percentages for each interval

plot

whether to plot the centles. This option is usefull if the sample statistics only are to be used

...

for extra arguments

Value

• Centile plots are produced and the sample centiles below each centile curve for each of the r ranges of x can be saved into a matrix.

Warning

This function is appropriate when only one continuous explanatory variable is fitted in the model

References

Rigby, R. A. and Stasinopoulos D. M. (2005). Generalized additive models for location, scale and shape,(with discussion), Appl. Statist., 54, part 3, pp 507-554. Stasinopoulos D. M., Rigby R.A. and Akantziliotou C. (2003) Instructions on how to use the GAMLSS package in R. Accompanying documentation in the current GAMLSS help files, (see also http://www.gamlss.org/). 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

gamlss centiles, centiles.com

Examples

data(abdom)
h<-gamlss(y~pb(x), sigma.formula=~pb(x), family=BCT, data=abdom) 
mout <- centiles.split(h,xvar=abdom$x)
mout
rm(h,mout)