Perhaps I was in an extremely corrupt environment (which eventually made me leave), but I would put the "intentional fraud" rate as high as 30% or so. I pointed out one of such instances
once and that was the beginning of the end for me in that place.
More: My field was Biology. No one double checks anyone or anything. A measurement comes back and you can just pretty much ignore it, in the end you just write whatever you need for your thesis to hold (I mean not me, but that's pretty much everybody's dirty secret). In the rare case that someone actually wants to check it out (1 in 1,000), you can just say that the "original data was lost". Sometimes the only thing you can trace back is some sort of written journal, in which anybody could write anything and that doesn't make it true/false.
Not long ago, there was a group of scientists that went on to try to replicate some landmark results on cancer research (I'll update with a good reference if I find it) and found out that only a very low number of them matched their observations. Some of those were not even close ... like, waaaay outside a very generous experimental margin of error.