 Scientists such as Donovan Rawcliffe (1952), C. E. M. Hansel (1980), Ray Hyman (1989) and Andrew Neher (2011) have studied the history of psi experiments from the late 19th century up until the 1980s.In every experiment investigated, flaws and weaknesses were discovered so the possibility of naturalistic explanations (such as sensory cues) or deception and trickery were not ruled out.The data from the Creery sister and the Soal-Goldney experiments were proven to be fraudulent, one of the subjects from the Smith-Blackburn experiments confessed to fraud, the Brugmans experiment, the experiments by John E. Coover and those conducted by Joseph Gaither Pratt and Helmut Schmidt did not rule out the possibility of sensory cues or trickery.