No, it's the value of '1' SAS that's the issue. SAS doesn't find any values that are 1 to be the reference. This could be either because you have no 1s in your data set or because you have a format applied to the VAR4 variable that displays the 1s as "Yes" for example. If the variable has a format, REF expects the formatted value, not the unformatted value. But we're guessing a bit. The log and the results from the code I included would allow us to definitively answer your question.
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