Which of the following can challenge the validity of an expert witness?

The ability to challenge the validity of an expert witness is primarily vested in another expert witness with opposing views. In legal proceedings, expert witnesses provide specialized knowledge to assist the court in understanding complex issues. When one party presents an expert witness, the opposing party can bring in another expert to critique the first expert's qualifications, methodology, or conclusions. This cross-examination through alternative expert testimony is fundamental as it allows for a thorough examination of evidence and encourages the evaluation of conflicting opinions, which can help the judge and jury make informed decisions.

Other parties, such as the judge, may have a role in assessing the qualifications of an expert witness, but the most direct challenge comes through competing expert testimony. Family members of the defendant and court reporters do not have the role of evaluating or contesting the expert witness's validity; their involvement is either peripheral or administrative in nature. Thus, the participation of another expert witness with differing views is the most recognized and formal method of challenging the credibility and reliability of an expert witness in court.