Most responders honor the "rules of the game" and respond to questionnaires only once. Unfortunately sometimes when a sensitive issue is in question and the results might affect someone, one might try to bias the results by sending multiple responses.

Depending on the questionnaire configuration we use different means to identify and avoid such situations, though not all means are as reliable.

In this option our system keeps track on all users that responded and make sure that each user responds only once to each questionnaire. This option can be applied only when the questionnaire is configured to accept only registered members or invited user .

Theoretically some people might register multiple times and identify themselves by a different mailbox each time if they own more than one mailbox, but this is not likely to happen much. The invitation service solves this problem completely and exempt the users from the need to register.

In this option we put a small piece of information (a.k.a. a cookie ) in the browser, so the next time a user is trying to send a response the browser also sends this information back and we can know that this is not the first time. This is the default option when the Email Tracking cannot be applied. Unfortunately this option is not very reliable and it won't work if the user uses a different browser (e.g. using a different computer) or if the user configures the browser to clear cookies. Although this option is not as reliable as the Email Tracking it is commonly much more comfortable to all parties since the responders are not required to register and the publishers are not required to send invitations.