Expert witnesses: must have qualifications in relevant subject area (education and/or experience); must testify on proper subject matter (scientific, technical, or specialized knowledge that will be helpful in deciding a fact); must base opinion on “reasonable degree of probability or reasonable certainty” and on personal knowledge, evidence in trial records, or facts outside he records if of a type reasonable relied on by experts in the field (cannot read this to the jury, may only state in general terms what he relied on); the opinion must be reliable determined by testing of principles or methodology, rate of error, acceptance in the discipline, and peer review/publication.