Contributed by Colleen Carlin:
Just finished virtually attending a webinar titled "Detecting and Rejecting Duplicate Responses in Online Surveys" presented by Bill MacElroy of Socratic Technologies. This problem major risk with high incidence populations, but when we are after low incidence, frequently surveyed respondents the risk might be substantial.
Based on Bill's experience there are five key elements to examine prior to letting a respondent begin a survey that he claims will guarantee a 99 percent detection rate of duplicate respondents.
- Cookie match. This presumes that one routinely places cookies on respondent PCs and that the survey software always checks for it.
- IP address – which provides a geographic match
- Browser string . This refers to a standard set of configuration information that is easily captured off of a respondent's browser.
- Language setting of machine
- Client machine status – machine level data
All of these items provide a virtual 'fingerprint' of a particular machine and combined can be extremely effective at detecting duplicate respondents. At least according to Bill MacElroy.