Respondent passwords address the fundamental conflict between anonymity and security against manipulation of survey results.
If the questionnaire can be filled in by anybody who knows its URL, and at the same time respondents are anonymous, there is no guarantee against single respondents entering an extreme opinion multiple times with the aim of manipulating the survey results.
While it is possible to detect and correct this kind of manipulation by analyzing IP addresses, submission times, by using the "sorting by similarity" feature of the raw reports page, and finally, by deleting the invalid responses, it might be desirable to make this kind of attack impossible in the first place, without giving up the anonymity of respondents.
This can be done by using Respondent Passwords. The steps are:
Generating or Deleting Respondent Passwords
Creating new passwords is easy - just enter the desired number of passwords and click on the button.
If you want to unlock the questionnaire and make it again possible to answer without entering a password, delete all respondent passwords by clicking on the "Delete all passwords" button.
Downloading Respondent Passwords
Click on the link containing the number of unused passwords to download them all in one text file.
The passwords are user-friendly: they are not too long (just 6 characters), and they don't contain any characters that look too similar, for example lower-case l, capital I, and the digit 1.