My apologies for the messages on this. I just reran both commands and everything worked as advertised. Beats me what happened the first time - perhaps something was not saved - but I will remember to quit R and redo everything before bothering the list in future. --Naomi Naomi S. Altman 814-865-3791 (voice) Associate Professor Bioinformatics Consulting Center Dept. of Statistics 814-863-7114 (fax) Penn State University 814-865-1348 (Statistics) University Park, PA 16802-2111