These studies are bs because they capture corellations and confuse them with causations.

Good studies need controlled laboratory conditions to remove external variables.

For example, maybe FP projects are written by coders who have more years of experience on average. So in that case it's not about the language paradigm, any facts derived from the study would actually be about the individuals who write in that language. And it's not surprising at all that more experienced individuals write fewer bugs. This is just one factor that may be ignored; there are probably hundreds that can cause significant distortions in the results.

It would be like saying that Norwegian is a highly effective language because they have a very high GDP per capita. This completely ignores the more significant fact that the country has vast amounts of offshore oil to capitalize on.