Traditional formulas for estimating the reliability of a composite test from its internal item statistics are in appropriate to judge the reliability of multiple regres sions and other weighted composites of subtests that are appreciably nonequivalent. Formulas are provided here for the reliability of such a composite given the reliabilities of its component subtests, followed by a comparison of the composite's reliability to that of its components. Compositing can easily incur a substan tial loss of reliability, though gains are entirely possi ble as well.
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