Assuming r, sd1 and sd2 as known(fixed) components, this works: X <- pnorm(q=q,sd=sd1)*r+pnorm(q=q,sd=sd2)*(1-r) uniroot(function(x)pnorm(q=x,sd=sd1)*r+pnorm(q=x,sd=sd2)*(1-r)-X,c(-1e6,1e6))
Cheers Am 12.12.2013 15:58, schrieb Johannes Radinger: > Thanks for the fast response. Of course I totally overlooked qnorm as I had > a more complex task in my head. > > I wanted to reverse following equation: > r=0.67 > q=-150 > sd1=100 > sd2=1000 > > X <- pnorm(q=q,sd=sd1)*r+pnorm(q=q,sd=sd2)*(1-r) > > Maybe its mathematically really easy, but somehow I don't get it how to do > reverse and provide X and > get q especially with the presence of r respectively as weighting factors > for the two distributions. > > /J > > > On Thu, Dec 12, 2013 at 3:09 PM, Dániel Kehl <ke...@ktk.pte.hu> wrote: > >> Looks like homework. >> >> Try ?qnorm >> ________________________________________ >> Feladó: r-help-boun...@r-project.org [r-help-boun...@r-project.org] ; >> meghatalmazó: Johannes Radinger [johannesradin...@gmail.com] >> Küldve: 2013. december 12. 14:56 >> To: R help >> Tárgy: [R] Solving a normal distribution pnorm for q >> >> Hi, >> >> >> >> I found follwowing example of pnorm here: >> >> >> http://www.r-tutor.com/elementary-statistics/probability-distributions/normal-distribution >> >> >> >> Problem >> >> Assume that the test scores of a college entrance exam fits a normal >> distribution. Furthermore, the mean test score is 72, and the standard >> deviation is 15.2. What is the percentage of students scoring 84 or more in >> the exam? >> >> >> >> Solution >> >>> pnorm(84, mean=72, sd=15.2, lower.tail=FALSE) >> >> [1] 0.21492 >> >> >> >> That is straight forward, however what if I want to know the score the best >> 30% students are reaching at least. So I know the solution of pnorm but >> want to know its q. How can that be achieved in R? >> >> >> >> Any suggestions? >> >> >> >> /Johannes >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-help@r-project.org 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. >> > > [[alternative HTML version deleted]] > > > > ______________________________________________ > R-help@r-project.org 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. > -- Eik Vettorazzi Institut für Medizinische Biometrie und Epidemiologie Universitätsklinikum Hamburg-Eppendorf Martinistr. 52 20246 Hamburg T ++49/40/7410-58243 F ++49/40/7410-57790 -- Besuchen Sie uns auf: www.uke.de _____________________________________________________________________ Universitätsklinikum Hamburg-Eppendorf; Körperschaft des öffentlichen Rechts; Gerichtsstand: Hamburg Vorstandsmitglieder: Prof. Dr. Christian Gerloff (Vertreter des Vorsitzenden), Prof. Dr. Dr. Uwe Koch-Gromus, Joachim Prölß, Rainer Schoppik _____________________________________________________________________ SAVE PAPER - THINK BEFORE PRINTING ______________________________________________ R-help@r-project.org 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.
