Judge Denver D. Dillard was trying to decide whether a slow-witted Iowa man accused of acting as a drug mule was competent to stand trial. But the conclusions of the two psychologists who gave expert testimony in the case, Judge Dillard said, were “polar opposites.”

One expert, who had been testifying for defendants for 20 years, said the accused, Timothy M. Wilkins, was mentally retarded, had a verbal I.Q. of 58 and did not understand the proceedings.

The prosecution expert, who had testified for the state more than 200 times, said that Mr. Wilkins’s verbal I.Q. was 88, far above the usual cutoffs for mental retardation, and that he was competent to stand trial.

Judge Dillard, of the Johnson County District Court in Iowa City, did what American judges and juries often do after hearing from dueling experts: he threw up his hands. The two experts were biased in favor of the parties who employed them, the judge said, and they had given predictable testimony.