Stop people from submitting a Google Form more than once

This article explains how to stop more than one person providing a response to a questionnaire that you have made using Google Forms.

Previously I've shown how to use Google Forms to put a survey or questionnaire into your blog.

Sometimes when you put a form into a blog-post, it is OK for people to respond more than once - and Forms even has an option to submit another entry immediately.

But sometimes it's not.

For example, if you are researching a particular topic, you probably want each person's opinion to count once, rather than having an enthusiastic person (effectively a human bot) enter their responses many times and so bias your results.

Google Forms has now a feature which lets you require everyone who wants to submit results to your survey to be logged in to a Google account, and then only lets each Google Account submit the form once.

How to stop people submitting a Google Form more than once

Follow these steps to stop the same user entering a form multiple times:

1. Edit the form.
   
2. Click the Settings bar
   
3. Turn on the "Allow only one response per user" option.

Job done!   You will now only get one answer from each person.   Read one to find out more effects of doing this, and some more issues that you need to consider.

The effect of the one-response-per-user checkbox

When this option is turned in, each response is guaranteed to come from a unique Google-account.

People who want to respond to your form must log-in using a Google account before they can see the form.

The person's email address isn't recorded in the results sheet but Forms won't accept another entry from the same Google Account.

If someone tries to complete your Google Form again, a warning is shown, 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."

Is the Google account name available to the form-owner?

No. Google Forms checks the currently-logged-in account against the list of accounts that have submitted a response, but it does not display the account-names anywhere in the form results page.

Disadvantages of this approach

• People who do not have Google Account cannot use your form.

• People who are skeptical about linking their email address with their form entry may be unwilling to respond  - no matter how you try to re-assure them that you don't see it.

• Other's may think that you have their email address, and so get annoyed if you ask for it on your form.

• People who have multiple Google Accounts can still respond multiple times: a single person can control many different Google accounts, and could (if they were sufficiently evil / motivated) sign out and in again using each one to submit multiple results.

Are people who responded before the option was turned on counted?

No:   Google only tracks users who complete your form after the "Allow only one response per user" option is first turned on.   If you turn it on for an existing form, people will still have one more chance to respond.

However if you turn the option off and then on again, it does remember which Google accounts have responded during the time that the option was off, and stops them from responding again.

Some other things to consider

Is it really necessary

Some people may turn this option on because it seems like the right thing to do, even if it really doesn't not matter if someone entered more than one response. This could annoy some visitors - for example, someone who completes your questionnaire today, and then remembers later on that there is something else they would like to say.

My recommendation is that you should only use the Allow only one response per user option if it really makes sense for your form to be like this.   Otherwise, leave it turned off.

Don't let it stop YOU from testing your form

If your form is even slightly complicated, it is a good idea to test it (perhaps from a private test blog) before you start using it.

However if "Allow only one response per user" is turned on, then you will only be able to enter one response yourself.

The solution to this is to:

• Leave the option off while you are testing your form
• Only turn it on again just before you install the form it into your blog.

Other ways to guarantee unique responses

If you decide that allowing only one response per Google account is not a good approach for your form, then you may want to consider other ways of ensuring that each person only participates once. For example:

• Ask each person to enter their email address on the form, and only accept results from unique addresses. (But do remember that you cannot be certain that the addresses are associated with the people who provided them.)

• Make completing the form "inviation only" and email respondents a unique code that they have to input, then don't take account of any responses that don't have a valid code: you may need to enlist help from a neutral 3rd party to help with this, if you want respondents to believe that their input in anonymous.

• If your form is made with a Google Apps user-account, rather than a standard Google account, then you have an option to limit a Google Form to only accept responses from users who are in your domain - and if you do this, the responses-sheet records the person's username as well.
  
  So in this case, you could simply sort by user-name, and leave our responses where the one user-name responded more than once.

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