I do mean any statistics -- some controlled experiments, sieving through surveys, anything. I'm constantly being told old wives' tales by friends and old doctors' tales by doctors. I'm not asking for well-done science here, just if anybody has investigated anything at all -- any data.
A study done in 2001 ended with the conclusion:
This is not to say that the changes to the dental arches were positive or negative, but that there most certainly was an impact. Note that "digit sucking" means thumb sucking.
Another study had similar results:
Length of how long pacifier is used matters:
There seem to be no shortage of studies done in this matter.