You have created a survey using Google Forms but people have quickly figured out a way to game your poll and tilt the results in their favor. They are submitting multiple entries, and because Google Forms will not record the I.P. address or the email of the form submitter, it is nearly impossible for you to separate the duplicate submissions from the genuine entries.
How do you restrict Google Forms to only allow a single entry from a user?
If you are a Google Apps user, you can always restrict the Google Form to accept entries only from users who are part of your domain and the response spreadsheet will then record the username of the form submitter. However if you have a regular Gmail / Google Account, you have another option now to prevent multiple form submissions from the same user.
While creating the Google Form, click the Settings bar and turn on the option that says “Allow only one response per user.” When the unique option is enabled for a Google Form, respondents will have to sign-in with their Google account to access the form. Their email address won’t be recorded in the response sheet but Google Form will not allow another entry from the same Google Account.
If someone tries to fill the Google Form again, a warning message will be displayed saying “You’ve already responded. You can only fill out this form once. Try contacting the owner of the form if you think this is a mistake.”
This is by far the easiest approach though it does put your Google Form out of reach of people who do not have Google Account or those who are skeptical of associating the email address with their form entry (though this association is completely hidden from the form owner).