res=c(rnorm(1000,20,2),rnorm(1000,15,1.5),rnorm(1000,25,2.5),rnorm(1000,25,2.5))

###fatores

fac=c(rep("F1",1000),rep("F2",1000),rep("F3",1000),rep("F4",1000))

fac=factor(fac,levels=c("F1","F2","F3","F4"),labels=c("F1","F2","F3","F4"))

###gráfico em lattice

require(lattice)

histogram(

~res|fac,

xlab="Resultado",

ylab="Freqüência",

type=c("count"),

layout=c(1,4),

endpoints=c(0,40),

nint=30,

scales=list(x=list(at=c(0,10,20,30,40))),

panel = function(x, ...) 

{ 

panel.histogram(x,col=rgb(62,88,172,max=255),...) 

panel.abline(v=20,col=rgb(13,141,70,max=255),lwd=2)

} 

)