MEDICINE'S DATA GAP Across the country, doctors are struggling to decide which pain relievers to prescribe now that they know that popular drugs like Vioxx and Celebrex pose potentially serious heart risks. "We are desperately in need of information," said Stephen Brenner, an internist in New Haven. Yet for at least two years, doctors at the Mayo Clinic, the federal Veterans Affairs Department and the Kaiser Permanente health plan have been sharply limiting their use of Vioxx and Celebrex. That is because those three institutions, after undertaking separate reviews of test data available on various painkillers, reached the same conclusion:...