I am using a unique ID for individuals in a study. The ID must be between 001 and 150 and it is a 3-character string field to ensure 054 is entered, for instance, rather than 54. Certain numbers can be entered with fewer than 3 digits without generating an error message. Without trying every possible combination, it seems that these numbers are 1, 10, 11, 12, 13, 14 and 15. The thing that these seven numbers have in common is that they could all be extended to 3 digits by filling in only zeroes, and still meet the criteria for the field (100, 100 again, 110, 120, 130, 140, 150). 160 is too big for the range, so 16 generates an error message. 200 is too big, so 2 is not allowed. This is just a guess to explain why these seven numbers slip through the filter. If I'm right, is there anything I can do about it? If I'm wrong, what's the explanation? Thanks for your help, Vicky Simms
King's College London