In various legal settings, from courts to arbitrations and mediations, any person who has relevant "knowledge, skill, experience, training, or education" may qualify to testify as an expert. You can find that quotation in Rule 702 of the Federal rules of Evidence. However, a productive expert witness has to know more than just his or her own area of experience. You have to understand the overall legal framework. The rule also specifies that the expert witness has to apply that knowledge and those experience in ways to qualify both you as the expert and your work. First, you must base your testimony on "sufficient facts or data." As a specialist witness, you have to convince the court that those facts provide a solid basis for your opinions. You may not just rely on instincts or your experience in the industry.
Federal Rule of Evidence 702 is closely connected in law to the Daubert guideline that expert witnesses are expected to understand. You must determine the set of facts and data that will support any conclusions reached. To guide you, Rule 702 adds that your testimony must be "the product of reliable principles and methods." As an expert in the field, you should already be familiar with the principles and methods used by others in your field. Be prepared to reference and explain any commonly accepted regulations, standards, or guidelines that govern your industry. Finally, the rule dictates that you have to have "applied the principles and methods reliably to the facts of the case."
You will hear the name Daubert frequently when speaking with attorneys. You, and the attorneys with whom you work, must anticipate legal challenges to the acceptability of investigations and analyses. Daubert standards and challenges guide what you, as a specialist witness, must understand and how you should conduct your investigations, testing, and analyses.
You should also realize that expert witnesses have to function as part of a team. Competitive sports have sides – one opponent against another opponent. Lawyers admit that the judicial arena is also adversarial; while a trial is not a game, gamesmanship is involved. You can play in a pickup game, but it takes advanced skills to play in the major leagues. No matter what your specialty, becoming an expert witness in your specialty is the 'major leagues' for you.
You could be hired by either the defense or the plaintiff / prosecution. In criminal cases, the 'prosecution' is the party that brings the lawsuit; in civil cases, the 'plaintiff' is the party that brings the lawsuit.
Always working for defense attorneys or for plaintiff attorneys suggests bias, and I have found that attorneys perceive me as objective because I've worked on both sides of cases. This, in turn, has led to more casework. If you choose to always work for one side or the other, even for what seem to be good reasons, doing so will restrict your choices and your future work. As an expert witness, you can offer objective analytical skills to attorneys on both sides of any case.
A good thing to remember as an expert witness is, as defense attorneys say, all defendants are entitled to a legal defense and are innocent until proven guilty. You do not resolve the right or wrong of a case. You bring your expertise and knowledge to the court, present your analysis and findings, and then provide impartial testimony.