In the late 1990s, the Texas Supreme Court indicated that the substance of an expert’s testimony must be considered, specifically the data the expert relies on to form his/her opinion. If the foundational data upon which the expert bases his opinion is unreliable, then the expert’s opinion will be considered unreliable.
Very often, in Texas pharmaceutical injuries or Texas wrongful death cases from exposures to lethal substances, the Court looks at epidemiological studies of the substance’s effect on a population. The study must demonstrate that the risk of disease or injury for the population of people exposed to the substance is twice the risk of the population contracting the same disease who have not been exposed to the substance.
To illustrate, if a disease naturally occurs in 6 out of 1000 people when they are not exposed to a certain drug or substance, then a study would have to show that more than 12 out of 1000 exposed to the drug or substance would suffer the disease. Another option is that the epidemiological study must show significant results at a 95% confidence level.