Mrs. Zuchowicz (P) filed a prescription for the drug Danocrine at the Naval Hospital. It erroneously instructed P to take 1600 milligrams per day. This was twice the maximum recommended dosage. P took the overdose each day for a month. During that time, she experienced abnormal weight gain, bloating, hot flashes, night sweats, a racing heart, chest pains, dizziness, headaches, acne, and fatigue. She reduced the dosage in half for a week and then she was examined by a private physician and was told not to take the drug anymore. She was diagnosed that summer with pulmonary hypertension. Her life expectancy was 2.5 more years. P was on the waiting list for a heart-lung transplant when she became pregnant. She gave birth to her son but became ineligible for a heart-lung transplant while she was pregnant. P died the next month. P claimed to have developed primary pulmonary hypertension, a fatal lung condition as a result of her taking that much medicine. P sued the United States (D) under the Federal Tort Claims Act, 28 U.S.C. Sections 1346(b), 2671-2680. P died in 1991, and her husband continued the case on behalf of the wife's estate. Expert testimony revealed that the drug P took was responsible for her fatal disease. The doctor did not rule out all other possible explanations for P's condition, but he did exclude all other causes of secondary pulmonary hypertension. The doctor also ruled out all previously known drug-related causes of PHH. The doctor then correlated P's good health and the subsequent poor health and symptoms almost immediately occurring right after P took the overdose of drugs; this was typical of drug-induced PHH. The rarity of PPH, combined with the fact that so few human beings have ever received such a high dose of Dancing, impacted on the manner in which P could prove causation. The number of persons who received this type of overdose was simply too small for P to be able to provide epidemiological, or even anecdotal, evidence linking PPH to Danocrine overdoses. P based his case primarily on the testimony of two expert witnesses, Dr. Richard Matt hay, a physician and expert in pulmonary diseases, and Dr. Randall Tackett, a professor of pharmacology who has published widely in the field of the effects of drugs on vascular tissues. In rendering a judgment for the plaintiff, the district court relied heavily on the evidence submitted by these two experts. D challenges both the admissibility and the sufficiency of their testimony. P got the verdict and D, and P appealed.