I want to create a survey where each potential respondent will have an id number that they will enter (9 digits or less). I don't need to validate the id. But I want to prevent reuse of the same id number. If a user completes the survey using one id number, he or she can complete the same survey again later using a different id but not the old id.

ID numbers are not stored in a database. The id numbers are not known in advance to the researcher, so it is not possible to use tokens.

The first question in the survey will ask them to enter the id number. If the id has not been previously used and the id format is correct, they will be allowed to proceed further. Otherwise, they will be sent to an end page with a "sorry" message.

Has anyone attempted anything like this? Can someone give me some ideas on how to do this?

Thanks very much.

You cannot directly access answers from previous surveys.

You will need to make an AJAX call to a remote PHP script that tests the input id against previous answers. If a match is found, you can use JavaScript to toggle a hidden radio question and apply a quota of 0 to that question.

Thanks very much.