On 5/6/2013 7:02 AM, arun wrote: stErr<- sd(vec1)/sqrt(length(vec1)) Or possibly, stErr<- sd(vec1)/sqrt(!is.na(vec1)) -- Robert W. Baer, Ph.D. Professor of Physiology Kirksille College of Osteopathic Medicine A. T. Still University of Health Sciences Kirksville, MO 63501 USA