How should multiple Mechanical Turk research subjects from the same IP address be handled? I saw this question on Twitter from Jay Van Bavel (@jayvanbavel), and thought it was a good fit for the site.


  Does anyone find that multiple subjects from the same IP address in
  their #MTurk data? How do you deal with this issue? Citations welcome.


Thus, to rephrase:


What does it mean when you get two or more Mechanical Turk participants in a study with the same IP address?
What is a general strategy for dealing with such cases?
Are there are any references discussing the issue?
I'll address just the first of your three sub-questions, the others have been answered by Chuck Sherrington.


What does it mean when you get two or more Mechanical Turk participants in a study with the same IP address?


IP addresses are rarely "fixed" to an individual computer. Each provider has a range of IP addresses available and assigns them to computers as they connect to the network. Every time you boot your computer, every time you connect to a WLAN network, you'll probably have a different IP address. Try it with a tool such as http://whatismyipaddress.com

So of course the IP address you had yesterday will be assigned to someone else tomorrow. It only means that both computers were connected through the same provider. No other conclusions can be drawn from the IP address!

(Only the combination of IP address and connection time is unique to your computer. Your provider stores your connection data for a legally specified period, and during this time the police will be able to identify your computer if they know the time of the connection, but this data is not publicly available.)

Usually IP addresses remain stable through a session, but you cannot even rely on that. DSL connections are often reset once every 24 hours, so if you are online at night, you might experience a loss of your network connection, and after that you'll very likely have a different IP. Mobile connections are separated much more often, and your IP address will change as often. So, if you save a user's IP address at the beginning of a survey and again at the end, both might differ! This will be especially true for users surfing through anonymisation tools such as a TOR network which are programmed to switch IP addresses regularly.

You cannot reliably identify a single computer through an IP address. Use cookies for that or rely on user specified data.



See https://en.wikipedia.org/wiki/IP_address#IP_address_assignment