[R] simulation-binomial

[Greg Snow]

Does this do what you want?

> x2 <- rbinom( 200, 1, ifelse(x, .95, p1/.6) )
> y2 <- rbinom( 300, 1, ifelse(y, .8, p1/.6) )

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
 
 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
> sigalit mangut-leiba
> Sent: Wednesday, August 08, 2007 11:18 AM
> To: r-help
> Subject: Re: [R] simulation-binomial
> 
> I have the probability: P(T+ / D+)
> i want to find P(T+,D+) which is: P(T+ / D+)*P(D+) and i have 
> those probabilities. i dont know how to write this in R.
> something like this: (say p2 is the conditional prob. and p1 
> is the joint
> prob.)
> 
> p2 <- p1/.6
> x <- rbinom(200, 1, .6)
> y <- rbinom(300, 1, .6)
> if (x) p2==0.95
> if (y) p2==0.80
> 
> i don't know how to write the "if "condition.
> thank you for your reply,
> sigalit.
> 
> 
> On 8/8/07, Kyle Henderson <ambertk at ohsu.edu> wrote:
> >
> > That depends on what you meant by writing the conditional 
> probability.
> > Bayes rule says that the probability of testing positive 
> when one has 
> > the disease is calculated as follows:
> >
> >      Pr(T+ | D+)=(Pr(D+ | T+)*Pr(T+))/Pr(D+)
> >
> > is that what you mean?
> >
> >
> > Kyle H. Ambert
> > Department of Behavioral Neuroscience
> > Oregon Health & Science University
> >
> >
> >
> >  On 8/8/07, sigalit mangut-leiba <smangut at gmail.com> wrote:
> >
> > > hello,
> > > i want to do a binomial simulation, by taking 200 var. from one 
> > > group
> > > (x)
> > > and 300 from another (y).
> > > the prob. for disease=.6 in both groups.
> > >
> > > x <- rbinom(200, 1, .6)
> > >
> > > y <- rbinom(300, 1, .6)
> > > if the person is from group x - the probability to find 
> the disease, 
> > > assuming the person is sick, is .95, if he is from group 
> Y its .80.
> > > i want to know the joint probability: p(the person has 
> the disease 
> > > and tested sick)=P(D+,T+).
> > > my problem is how to write the conditional prob.
> > > Thanks for your help, also reference on this subject (binomial
> > > simulation)
> > > would be great.
> > > Sigalit.
> > >
> > >         [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
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> self-contained, 
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> > >
> >
> >
> 
> 	[[alternative HTML version deleted]]
> 
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