title: How to prevent duplicates in online anonymous surveys?
body: <p>I am writing an online survey and I am wondering if there are any good techniques for allowing anonymous people to go to the survey and participate and also prevent duplicates.</p>
  
  <p>I have considered the following, but there are drawbacks from each:</p>
  
  <ul>
  <li>Use cookie in browser</li>
  <li>Record IP address</li>
  <li>Compare answers for similarities along with either/or the first two methods</li>
  </ul>
  
  <p>Of the techniques I have considered, you either prevent multiple people from using the same device, or make it easy for a user to duplicate survey results.  Hopefully someone has an excellent way to prevent this :)</p>