Experts provide important inputs in arbitrations and litigations (lawsuits). Their input/counsel gives the fact-finder an objective rendition of the facts and assessment of those facts, and facilitates fair adjudication of the dispute/lawsuit.
Here is the legal background on expert analysis and witnesses. As a matter of general practice, per Federal Rule of Evidence 602, courts prohibit witnesses from testifying based on their own opinions or analysis. However, courts permit expert witnesses testifying about matters within their field of expertise. A witness is deemed to be an expert witness by virtue of education, training, skill, or experience, is believed to have expertise and specialized knowledge in a particular subject beyond that of the average person, sufficient that others may officially and legally rely upon the witness's specialized (scientific, technical or other) opinion about an evidence or fact issue within the scope of his expertise, referred to as the expert opinion, as an assistance to the fact-finder. One of the major attribute of an expert is recognition by his/her professional peers.
Generally speaking, experts may testify about their conclusions in a case so long as their analysis is scientifically sound. In reaching their conclusions, experts may rely on the same sorts of evidence that people in their profession normally rely on in their work, even if the evidence is otherwise inadmissible in court.
In the federal courts, judges determine the credibility of expert witnesses in a pre-trial hearing. In considering witnesses' qualifications, judges may consider information that is not admissible as evidence. Before trial, all experts must prepare a report summarizing their analysis and conclusions, and share the report with all other parties. This allows other parties to effectively cross-examine the expert.