1. Keep meticulous records of all emails and answers received while screening research study applicants over the phone—our earliest records date back to 2005.
2. Anytime someone applies for a study, search that person's name, email address/es, and most importantly, phone number/s using your operating system's search engine, email search engine, or any other, equivalent search engine.
Do NOT skip the phone number during your research. Try different formatting styles for the same phone number, for example: 617.123.4567; 617-123-4567; 617 123 4567. It's easy for anyone to give a phony name, a different age, a false profession—even a new email address—but it's not easy to change phone number too often. That's the piece of information that will remain unchanged for relatively long periods of time.
3. Read the answers you have received from the same applicant through the years and make sure they are consistent through time. Those applicants who exhibit a pattern of changing their data—name, age, email address, marital status, phone model, car, profession, etc.—are very likely to be chronic liars.
4. If you use online surveys to pre-screen the applicants, check if the same IP address appears associated to different people in different moments in time (see point 2 above). If that's the case, it should raise a flag of suspicion, although after further investigation you might find out that it was just another member of the same household who previously applied from the same IP address. Note: Most online survey websites will include the responders' IP addresses in the set of data you can download from them.