DETAILS The PATTERN function returns 0 or 1 (not undefined as it should) when the first argument is a missing value. In this case the function is looking at some random memory which may or may not include the pattern to be matched. EXAMPLE PROGRAM program string x missing values x ("NA") set x ("NA") write [PATTERN(x,"TABLE")] [PATTERN(x,"CHAIR")] end program WORKAROUND Check if aguments are missing before using PATTERN