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Critical Ratio

Critical Ratio (CR): A mathematical quantity used to decide whether the size of the observed deviation from chance in a psi test is significantly greater than the expected degree of random fluctuation about the average; it is obtained by dividing the observed deviation by the standard deviation; also called the z statistic.


  1. Parapsychology by Michael A. Thalbourne, Republished by Puente Publications, Charlottesville, VA, USA, 2003