Arthur R. Jensen

“Should the discovery of fire have been avoided because arsonists can misuse it? Any kind of information can be misused by those who are determined to do so. The place to stop the misuse of knowledge is not at the point of inquiry, but at the point of misuse.”
― Arthur R. Jensen, Straight Talk About Mental Tests

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It is a common misconception that psychological measurements of human abilities are generally more prone to error or inaccuracy than are physical measurements. In most psychological research, and especially in psychometrics, this kind of measurement error is practically negligible. If need be, and with proper care, the error variance can usually be made vanishingly small. In my laboratory, for example, we have been able to measure such variables as memory span, flicker-fusion frequency (a sensory threshold), and reaction time (RT) with reliability coefficients greater than .99 (that is, less than 1 percent of the variance in RT is due to errors of measurement). The reliability coefficients for multi-item tests of more complex mental processes, such as measured by typical IQ tests, are generally about .90 to .95. This is higher than the reliability of people's height and weight measured in a doctor's office! The reliability coefficients of blood pressure measurements, blood cholesterol level, and diagnosis based on chest X-rays are typically around .”
― Arthur R. Jensen, The g Factor: The Science of Mental Ability