if you go x[i] you are giving x an "index vector", which we had mistakenly thought was an integer. Rather, it is a vector of indices for observations. Here's data x <- c(1 , 4, 3, 2, 5) x[1] would be 1 x[2] would bd 4 but if you put an "index vector" in the brackets, you have x [ c(1,2,1,2] ] it means take the first, the second, the first, the second, so x [ c(1,2,1,2] ] is 1, 4, 1, 4 So in the procedure diff.ttest, when we have x[i] and y[i], we mean "take the vectors x and y after grabbing the index values selected for each resample" That page I sent you a minute ago is from R by Example, which I think is quite great. http://www.mayin.org/ajayshah/KB/R/index.html pj
Paul E. Johnson email: pauljohn at ku.edu Dept. of Political Science http://lark.cc.ku.edu/~pauljohn 1541 Lilac Lane, Rm 504 University of Kansas Office: (785) 864-9086 Lawrence, Kansas 66044-3177 FAX: (785) 864-5700