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 [EMAIL PROTECTED] (801) 408-8111 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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]] > > > > > > ______________________________________________ > > > R-help@stat.math.ethz.ch mailing list > > > https://stat.ethz.ch/mailman/listinfo/r-help > > > PLEASE do read the posting guide > > > > http://www.R-project.org/posting-guide.html<http://www.r-project.org > > > /posting-guide.html> and provide commented, minimal, > self-contained, > > > reproducible code. > > > > > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
