R help - Nov 2007 - rbinom with computed probability

Hello,
I have a loop with probability computed from a logistic model like this:
for (i in 1:300){

p[i]<-exp(-0.834+0.002*x[i]+0.023*z[i])/(1+exp(-0.834+0.002*x[i]+0.023
+z[i]))

x and z generated from normal distribution.
I get 300 different probabilities And I want to generate variables from
bernulli distribution
with P for every observation:

T[i]<-rbinom(1,1,p[i])
But i get missing values for T.
What I'm doing wrong?
Thank you,
Sigalit.

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I don't run into problems doing this:

x=rnorm(300)
z=rnorm(300)
for (i in 1:300){
  p[i]<-exp(-0.834+0.002*x[i]+0.023*z[i])/(1+exp(-0.834+0.002*x[i]+0.023
+z[i])); T[i]<-rbinom(1,1,p[i])
}

hth, Ingmar

On 23 Nov 2007, at 10:25, sigalit mangut-leiba wrote:
> Hello,
> I have a loop with probability computed from a logistic model like  
> this:
> for (i in 1:300){
>
> p[i]<-exp(-0.834+0.002*x[i]+0.023*z[i])/(1+exp(-0.834+0.002*x[i]+0.023
> +z[i]))
>
> x and z generated from normal distribution.
> I get 300 different probabilities And I want to generate variables  
> from
> bernulli distribution
> with P for every observation:
>
> T[i]<-rbinom(1,1,p[i])
> But i get missing values for T.
> What I'm doing wrong?
> Thank you,
> Sigalit.
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting- 
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Ingmar Visser
Department of Psychology, University of Amsterdam
Roetersstraat 15
1018 WB Amsterdam
The Netherlands
t: +31-20-5256723



	[[alternative HTML version deleted]]

G'day Sigalit,

On Fri, 23 Nov 2007 11:25:30 +0200
"sigalit mangut-leiba" <smangut at gmail.com> wrote:
> Hello,
> I have a loop with probability computed from a logistic model like
> this: for (i in 1:300){
> 
> p[i]<-exp(-0.834+0.002*x[i]+0.023*z[i])/(1+exp(-0.834+0.002*x[i]+0.023
> +z[i]))
> 
> x and z generated from normal distribution.
> I get 300 different probabilities And I want to generate variables
> from bernulli distribution
> with P for every observation:
> 
> T[i]<-rbinom(1,1,p[i])
> But i get missing values for T.
> What I'm doing wrong?
I guess the problem is that in the numerator you have "0.023*z[i]" but
"0.023+z[i]" in the denominator.  Thus, some p[i] can be outside of
[0,1] which would produce NAs in T.

But why a for loop? This code is readily vectorised:

p <- exp(-0.834+0.002*x+0.023*z)/(1+exp(-0.834+0.002*x+0.023*z))

HTH.

Cheers,

	Berwin

=========================== Full address ============================Berwin A
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