There are actually some studies conducted. Note that these are _suspected_ interference from personal electronic devices and also incidents with passengers unwilling to turn them off: http://asrs.arc.nasa.gov/docs/rpsts/ped.pdf

Of course, all of this is anecdotal so it won't fly here on HN. :)

The real difficulty is that when an instrument malfunctions, that can be for any number of reasons. It's not unusual for malfunctions to occur, which is why airplanes have redundant avionics. However, there seems to be a few instances where the interference stopped after a passenger turned off their devices.