I am comparing two data sets using proc compare. I am outputing results to display all three recods (base, compare, dif). For some reason, some 'base' and 'compare' records have a matching ID, but there is no Dif record displayed. About half my population is showing a "Dif' record in the out file, but for others is not. Can anyone offer any explanation as why this may be occuring. note: Data is sorted before compare.