Hi,
The probability of false detection is: P(T+ | D-)=1-P(T+ | D+)=0.05.
and I want to find the joint probability P(T+,D+)=P(T+|D+)*P(D+)
Thank you for your reply,
Sigalit.


On 8/13/07, Moshe Olshansky <m_olshansky@yahoo.com> wrote:
>
> Hi Sigalit,
>
> Do you want to find the probability P(T+ = t AND D+ =
> d) for all the combinations of t and d (for ICU and
> Reg.)?
> Is the probability of false detection (when there is
> no disease) always 0?
>
> Regards,
>
> Moshe.
>
> --- sigalit mangut-leiba <smangut@gmail.com> wrote:
>
> > hello,
> > I asked about this simulation a few days ago, but
> > still i can't get what i
> > need.
> > I have 2 units: icu and regular. from icu I want to
> > take 200 observations
> > from binomial distribution, when probability for
> > disease is: p=0.6.
> > from regular I want to take 300 observation with the
> > same probability: p=0.6
> > .
> > the distribution to detect disease when disease
> > occurred- *for someone from
> > icu* - is: p(T+ | D+)=0.95.
> > the distribution to detect disease when disease
> > occurred- *for someone from
> > reg.unit* - is: p(T+ | D+)=0.8.
> > I want to compute the joint distribution for each
> > unit: p(T+,D+) for icu,
> > and the same for reg.
> > I tried:
> >
> > pdeti <- 0
> >
> > pdetr <- 0
> >
> > picu <- pdeti*.6
> >
> > preg <- pdetr*.6
> >
> > dept <- c("icu","reg")
> >
> > icu <- rbinom(200, 1, .6)
> >
> > reg <- rbinom(300, 1, .6)
> >
> > for(i in 1:300) {
> >
> > if(dept=="icu") pdeti==0.95
> >
> > if (dept=="reg") pdetr==0.80
> >
> > }
> >
> > print(picu)
> >
> > print(preg)
> >
> > and got 50 warnings:
> >
> > the condition has length > 1 and only the first
> > element will be used in: if
> > (dept == "icu") pdeti == 0.95
> > the condition has length > 1 and only the first
> > element will be used in: if
> > (dept == "reg") pdetr == 0.8
> >
> > I would appreciate any suggestions,
> >
> > thank you,
> >
> > Sigalit.
> >
> >       [[alternative HTML version deleted]]
> >
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> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained,
> > reproducible code.
> >
>
>

	[[alternative HTML version deleted]]

