I just found a completely charming study from 1977 that tested whether psychiatric patients with mind-reading delusions were really telepathic.
Telepathy in mental illness: deluge or delusion?
J Nerv Ment Dis. 1977 Sep;165(3):184-200.
The belief that one can read others’ minds has long been considered a symptom of psychosis, despite reports in the parapsychological literature of veridical telepathy. All patients admitted to an inpatient psychiatric unit were screened for paranormal beliefs, and those claiming telepathic abilities were tested in a free-response ESP task. Eighteen per cent of the inpatient population claimed telepathic abilities; of the nine patients who completed the task, none performed above chance expectations. Higher frequencies of paranormal experiences than those reported previously in the psychiatric literature were attributed to the context of the study. Schneider’s first rank symptoms and a belief in telepathy discriminated schizophrenics more reliably than other paranormal experiences. Possible psychodynamics of delusions of telepathy were discussed in view of the predominance of women and younger men reporting them, as were the possible effects of such research on patients’ delusions.
Link to PubMed entry for study.