I like that you give me more information about the way to interpretated the options "ca". Also, I like that you explain to me how can I do with the "NA" values. I apreciated you response Thank you Johana S?nchez Venezuela -------------- next part -------------- An HTML attachment was scrubbed... URL: https://stat.ethz.ch/pipermail/r-help/attachments/20010909/5c571463/attachment.html