I've come across the concept of mass psychogenic illness (MPI) quite a few times in discussions about religious experiences. After reading the Wikipedia article on MPI, I have doubts on the validity of MPI as a scientific hypothesis that makes falsifiable predictions. Quoting the research section of the Wikipedia article (emphasis mine):
Besides the difficulties common to all research involving the social sciences, including a lack of opportunity for controlled experiments, mass sociogenic illness presents special difficulties to researchers in this field. Balaratnasingam and Janca report that the methods for "diagnosis of mass hysteria remain contentious." According to Jones, the effects resulting from MPI "can be difficult to differentiate from [those of] bioterrorism, rapidly spreading infection or acute toxic exposure."
These troubles result from the residual diagnosis of MPI. Singer, of the Uniformed Schools of Medicine, puts the problems with such a diagnosis thus: "[y]ou find a group of people getting sick, you investigate, you measure everything you can measure . . . and when you still can't find any physical reason, you say 'well, there's nothing else here, so let's call it a case of MPI.'" There is a lack of logic in an argument that proceeds: "There isn't anything, so it must be MPI." It precludes the notion that an organic factor could have been overlooked. Nevertheless, running an extensive number of tests extends the probability of false positives.
Is mass psychogenic illness a falsifiable scientific hypothesis?