[R] basic plot() question

[Peter Dalgaard BSA]

Tord Snall <tord.snall at ebc.uu.se> writes:

> Dear all,
> I try to plot a logstic regression model as follows:
>  
> Valkror<- read.table("Valkror.txt", header=T)
> np.bark<- glm(Npinc~bark, family=binomial, data=Valkror)
> plot.formula(np.bark$fitted.values~ Valkror$bark)
> 
> The above looks nice but I want to connect the points with a line so I try:
> 
> plot.formula(np.bark$fitted.values~ Valkror$bark, type="b")
> 
> but it gives a somewhat! unexpected figure.     :(
> 
> Could someone please give a clue....

Not having your data, I can't see what is wrong with your plot, but
I'd wager that it is because the x values are out of sequence. You
could try 

Valkror2<-Valkror[order(Valkror$bark),]

and then

plot(predict(np.bark,Valkror2,type="response")~Valkror2$bark,type="b")

which is also safer than your strategy in case there are missing
values in your data.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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