The more you know about your respondents in advance, the less they will need to fill in. Even when you’re sending out a survey without using contacts, you can add information to identify respondents. Here’s how: use hidden questions that are automatically prefilled by the survey URL. Your respondents won’t see the questions, but they will be prefilled based on values sent as querystring parameters in the URL.
For example, you could distribute your survey via different channels (website, newsletter, Facebook …). Using a hidden question you can determine which channel generated the most respondents. Or add a tracking code, like a user id to identify the respondent later. You can prefill any question as long it is one of the 3 question types below. The information from the querystring parameters will be added in real time to your reports and you can filter on it.