the wittiest or more scientific/academic answer will win.
How many experimental psychologists does it take to change a lightbulb?
It takes at least two, so that you can check for inter-observer reliability in the measurement of whether the lightbulb has indeed been changed or not.
How many experimental psychologists does it take to change a lightbulb?
before or after the therapy session!???
one but he has to run through a maze first
Pi
An infinite number. Every new participant introduces observational uncertainty so that one cannot simultaneously tell the position and velocity of the sequence of movements required to change the lightbulb, or even exactly where the lightbulb is at the exact time of changing (Heisenberg). Using quantum methods, one can calculate the probability of the lightbulb being in the changed state; however, by not having a true outside observer who is then observed, ad infinitum, there arises the Schrodinger's Lightbulb phenomenon whereby the lightbulb is both changed and not changed. Developments in String Theory promise to unravel this mystery in years to come, but it is unlikely to help the experimental psychologists.
Seven. But the lightbulb has to want to be changed.
Only one, but the lightbulb has to really want to change.
One, but the lightbulb must really want to change.
