Hi,
do you know the parameters of the binomial variate? then maybe you could use something like the code below. as Petr pointed out, it is generally not guaranteed that you can create variates with any linear correlation (ie, depending on the parameters of the binomial) n <- 100 # how many variates # your binomial variate (example) size <- 10; prob <- 0.2 vecB <- rbinom(n, size = size, prob = prob) rho <- 0.75 # desired cor m <- 0.5 # mean and sd of Gaussian sig <- 2 rho <- 2*sin(rho*pi/6) # a small correction C <- matrix(rho, nrow = 2, ncol = 2) diag(C) <- 1; C <- chol(C) # (1) transform binomial to Gaussian X1 <- qnorm(pbinom(vecB, size = size, prob = prob)) # (2) create another Gaussian X2 <- rnorm(n) X <- cbind(X1,X2) # (3) induce correlation (does not change X1) X <- X %*% C # (4) make uniforms U <- pnorm(X) # (5) ... and put them into the inverses vecB1 <- qbinom(U[,1],size,prob) vecG <- qnorm(U[,2], mean = m, sd = sig) # check plot(vecB1,vecG) cor(vecB1,vecG) all.equal(vecB1,vecB) sd(vecG) (linear correlation is not affected by linear transformation, so you can enforce exactly your desired mean and standard deviation for the Gaussian by rescaling it in the end) regards, enrico > -----Ursprüngliche Nachricht----- > Von: r-help-boun...@r-project.org > [mailto:r-help-boun...@r-project.org] Im Auftrag von Shane Phillips > Gesendet: Montag, 25. April 2011 01:00 > An: R-help@r-project.org > Betreff: [R] Random Normal Variable Correlated to an Existing > BinomialVariable > > Hi, R-Helpers! > > I have a dataframe that contains a binomial variable. I need > to add another random variable drawn from a normal > distribution with a specific mean and standard deviation. > This variable also needs to be correlated with the existing > binomial variable with a specific correlation (say .75). Any ideas? > > Thanks! > > Shane > ______________________________________________ > 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. ______________________________________________ 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.
