Déjà vu (French for "already seen") is experienced in one form or another by a large number of people (a recent survey indicated the incidence to be around 63% of the adult American population, for example).
There are many forms of what one might call "déjà" experience (on page 10 in his 1983 book "The Psychology of Déjà Vu" Dr. Vernon Neppe lists 20 of them!). In this survey, though, we wish to study two main forms, namely "déjà vécu" ("already lived through") and "déjà visité" ("already visited"). For more information about these two forms, please see http://home.cc.umanitoba.ca/~mdlee/dejavu.htm.
At this point we lack empirical data on the incidence of these forms of déjà vu and also about how they are experienced. Here are some questions which will allow us to form more accurate picture of what various types of déjà experience are happening: