I have the following script for generating a dataset. It works like a champ except for a couple of things.
1. I need the variables "itbs" and "map" to be negatively correlated with the binomial variable "lunch" (around -0.21 and -0.24, respectively). The binomial variable "lunch" needs to remain unchanged. 2. While my generated variables do come out with the desired means and correlations, the distribution is very narrow and only represents a small portion of the possible scores. Can I force it to encompass a wider range of scores, while maintaining my desired parameters and correlations? Please help... Shane Script follows... #Number the subjects subject=1:1000 #Assign a treatment condition from a binomial distribution with a probability of 0.13 treat=rbinom(1*1000,1,.13) #Assign a lunch status condition froma binomial distribution with a probability of 0.35 lunch=rbinom(1*1000,1,.35) #Generate age in months from a random normal distribution with mean of 87 and sd of 2 age=rnorm(1000,87,2) #invoke the MASS package require(MASS) #Establish the covariance matrix for MAP, ITBS and CogAT scores sigma <- matrix(c(1, 0.84, 0.59, 0.84, 1, 0.56, 0.59, 0.56, 1), ncol = 3) #Establish MAP as a random normal variable with mean of 200 and sd of 9 map <- rnorm(1000, 200, 9) #Establish ITBS as a random normal variable with mean of 175 and sd of 15 itbs <- rnorm(1000, 175, 15) #Establish CogAT as a random normal variable with mean of 100 and sd of 16 cogat<-rnorm(1000,100,16) #Create a dataframe of MAP, ITBS, and CogAT data <- data.frame(map, itbs, cogat) #Draw from the multivariate distribution defined by MAP, ITBS, and CogAT means and the covariance matrix sim <- mvrnorm(1000, mu=mean(data), sigma, empirical=FALSE) #Set growth at 0 growth=0 #Combine elements into a single dataset simtest=data.frame (subject=subject, treat=treat,lunch, age=round(age,0),round(sim,0),growth) #Set mean growth by treatment condition with treatd subjects having a mean growth of 1.5 and non-treated having a mean growth of 0.1 simtest<-transform(simtest, growth=rnorm(1000,m=ifelse(treat==0,0.1,1.5),s=1)) simtest cor (simtest) ______________________________________________ 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.
