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type ?cor and read the help file In particular read it till you find the entry that tells you how to deal with missing observations. You need to do this because as you get more competent you will undoubdtedly come across other issues, so learning the format of the help and realising why you need to check the Arguments section will reduce your frustration in the future. You also need to read the posting guide to make sure that you don't put people offside by failing to follow a basic set of stan...