Robert Joiner (plaintiff) worked as an electrician for the Water and Light Department in Thomasville, Georgia. As part of his job, he came into frequent contact with a mineral-based dielectric fluid, used as a coolant. After several years, it was discovered this fluid contained significant amounts of hazardous chemicals. These chemicals were banned in the United States in 1978. Joiner continued working as an electrician, but in 1991, he was diagnosed with small cell lung cancer. Joiner sued General Electric Co (GE) (defendant) and Westinghouse Electric (WE) (defendant), both manufacturers of the dielectric fluid. In his complaint, Joiner linked his cancer to exposure to the fluid. However, Joiner had also been a smoker for eight years, and both his parents were smokers. There was also a history of lung cancer in his family. Although admitting he may have already been at a heightened risk for lung cancer, Joiner alleged his exposure to the fluid “promoted” his cancer. He stated that but for his exposure to the fluid his cancer likely would not have developed for many years, if at all. At trial, GE and WE presented expert testimony stating that there was no evidence Joiner was actually exposed to the hazardous chemicals, and there was no evidence of a link between exposure to the chemicals and small cell lung cancer. The district court admitted this testimony but excluded the counter testimony of Joiner’s experts on the ground that it did not rise above “subjective belief or unsupported speculation.” The court of appeals reversed after applying a “particularly stringent standard of review.” The United States Supreme Court granted certiorari on the issue of the standard of review.