In a Federal Tort Claims Act case governed by Illinois law involving medical malpractice during delivery that left Yong Juan Zhao’s son “S.” with a grievously, irreversibly injured right arm, a federal judge used a combination of predictions from two vocational experts — David Gibson for Zhao and Susan Entenberg for the United States — in calculating that $2.6 million was the appropriate amount of damages for the five-year-old’s loss of future income.As part of his calculations, Gibson testified that S.’s worklife …