Random identification numbers

Steve Simon

2004-07-26

Someone asked me today for a set of random numbers. The purpose was to create an ID code that could be used to track back to the original records to resolve any inconsistencies or ambiguities. You should not use a medical record number, of course, because sharing a patients medical record number is a violation of HIPAA regulations. What you need to do is to assign a different number and then keep a link between that number and the patient's medical record number in a secure location (like a locked filing cabinet).

Strictly speaking, the numbers do not need to be random. 1, 2, 3 would work just fine. But the person I was working with didn't want the record number to provide any clue as to whether the person appeared early in the study or late.

You can generate a nice random number in Excel using the RANDBETWEEN function. I used RANDBETWEEN (1000,9999) to create a set of random numbers with exactly four digits.

Be sure to check that list to make sure no duplicates appear.

Another approach that also would have worked is to sort the sequential numbers 1, 2, 3, etc. in a random order.

I have a page that describes some other approaches to generating randomization lists for assigning treatment versus control.

You can find an earlier version of this page on my original website.