This enables resume capabilities on non-unique "StartSurvey" URLs. If the respondent closes their browser and wants to come back and finish the same interview, all they need to do is re-click the original "StartSurvey" URL. This will read the local unique identifier found in the cookie in that user's browser and resume where they left off.
Feel free to test this using the below link:
What information is stored in the cookie?
We store the survey's name as the cookie's name. Additionally, we only store a single unique identifier value - see below screenshot for an example of what that looks like:
Design > Screen Mode > Options > Internet Options > Other Settings:
In this window, you can elect to turn cookies on/off for the survey, and dictate the duration the cookies will remain active in the respondent's browser before expiring.
Cookies are not a fool proof method of retaining uniqueness. If a respondent disables cookies, uses a different browser, clears their cookies, or uses a different device.. none of that uniqueness transfers over.
If you want full uniqueness for surveys, you should use our recommended "DoPanel" or "DoExternalPanel" invitations and not "StartSurvey" invitations.
Survey programmers should also be aware of GDPR and privacy practices before implementing this feature.