A defendant may be spared the death penalty because he is mentally deficient in one area, even if his IQ score falls in the normal range, the California Supreme Court decided Thursday.

The state high court’s unanimous ruling rejected an appeals court decision that "full scale" IQ scores — composites of tests of various mental faculties — are the best measure of intelligence. The justices said courts may give greater weight to one measurement of IQ over another and that the best way to measure intellectual functioning may vary from case to case.

The decision gives judges broader discretion to spare defendants from execution for reasons of mental impairment and clarifies a 2005 ruling that allowed death row inmates to challenge their sentences on the grounds of mental retardation. That decision was triggered by a 2002 U.S. Supreme Court ruling that barred execution of mentally retarded inmates.

Because the legal definition of mental retardation does not rely on a fixed IQ score, trial courts may give greater weight to certain kinds of

John Philipsborn, who represented an association of criminal-defense lawyers in the case, said the ruling will affect at least 28 death row prisoners and at least eight defendants who are claiming mental retardation prior to trial.