Here are the results of my first round of tests with "Enable token based persistence: No".

If participant ends survey without saving, the incomplete response is in the database but later disappears during the course of my tests but before the same participant completes the survey (must look into this a bit more). Clicking on the invite link will bring the participant back to the survey but the questions are empty. So you can go previous, next but without any questions to answer, very strange here.

If the participant saves the survey to resume later but did not opt for an email, the incomplete response is also in the database. The invite link brings participant back to the survey in progress without any need for name/password. I believe this is due to cookies.

Tried the above on a new browser, the invite link will load new survey with the option to load unfinished survey using name/password.

If participant resets browser and starts new survey again and completes it, the database will contain records for the completed survey and incomplete survey(s). Token use will be decreased correctly and in my case, no more uses so clicking on the invite link will not be able to start a new survey anymore.

Now I'm going to test with "Enable token based persistance: Yes" to see if there's any difference. I think I'll turn off cookies as that confuses things.

Tests continued...

I tried to set "Enable token based persistence" to "Yes" for an anonymous survey but was not able to do so as this parameter is not allowed for anonymous surveys. But then I realised that I managed to change that setting on my previous activated survey so I tried that; activate the survey first, then set "Enable token based persistence" to "Yes". That worked but I think it would be a bug. The setting would probably not have any effect since I've just got clarification that that means that there will be a link between the token and the response which is not allowed in anonymous surveys. Hope I haven't broken anything...

So the results...

If participant ends survey without saving, the incomplete response is in the database and when clicking on the invite link again, the survey resumes. I believe this is due to cookies although I turned that off! I tried in new browser, the invite link loads new survey. If I then complete the survey, the token will be used but the first incomplete response will remain, i.e., there are 2 responses, 1 complete and 1 incomplete (could be more if I kept restarting over with new browser).

I decided to stop testing there and just live with any incomplete responses.

Any advice on how to handle these issues would be much appreciated. So to summarise, we are doing token based anonymous surveys with resume allowed. How to prevent multiple incomplete responses in the database if participant starts over again after not saving?

Thanks all!

Karen