As an expert witness, you’ll want to equip yourself with a foundational understanding of the key elements every attorney must prove in each case. You may be called upon to help lawyers establish these points either as a consultant during case preparations or as an expert witness testifying during proceedings. The three basic legal concepts of liability, causation, and damages are a good place to start. Their definitions do vary slightly state by state, but still share essential concepts which govern every legal dispute.
What is Liability?
The legal concept of liability focuses on whether a defendant had a duty or responsibility to the plaintiff. In the U.S., plaintiffs must demonstrate that the defendant had an affirmative duty to them. The responsibility and duty of certain professions are well-settled. The doctor-patient, attorney-client, and guardian-ward are special relationships that come with duties of competency, confidentiality, and required skills and care. When a doctor provides medical care, for example, they must have the requisite skills and experience and exercise diligence in providing patient care.
How are Experts Involved?
In establishing liability, plaintiffs must first prove the existence of a professional or other duty owed them. For example, an attorney might require an expert to review the medical records in a medical negligence case to find evidence that the patient-doctor relationship existed. This might be as simple as finding documentary evidence that the plaintiff had several appointments with the doctor, the doctor made a diagnosis, and that they recommended surgery. Then, the attorney would need records that prove the patient entered the hospital, signed consent forms, and that the accused doctor performed the surgery.
Proving a duty to a patient exists can become more complicated in situations where a doctor consults a colleague on a patient’s case, unbeknownst to the patient, and without any patient interaction with the consulting doctor. Also, the liability of a doctor who gave a second opinion agreeing with the primary doctor’s diagnosis and surgery recommendation can be a big issue when it turns out both doctors misdiagnosed the problem and the plaintiff suffered injuries from an erroneous surgery.
Physicians who practice in the same medical field as the defendant typically serve as expert witnesses in cases like this example. The expert reports or testimony would go towards establishing whether the doctor upheld the duty of care and treatment with the degree of skill, care, and diligence as would a reasonably competent physician under the same or similar circumstances.
What is Causation?
Causation centers on proving that a defendant’s action or inaction caused the plaintiff harm. In many states, tort law causation has two elements: factual cause and proximate cause. Lawyers and experts often prove factual cause, also known as actual cause, with the “but-for” test. Plaintiff counsel shows that the tort would not have happened “but for” the defendant’s actions or omissions.
For example, a bus swerved and hit a car causing minor damage to the passenger door. Factually, it may not be hard to show the action of the bus driver caused the plaintiff harm. The law, however, also uses the proximate cause concept to establish the primary cause of an injury. A defendant cannot be held liable for totally unforeseeable injuries. The key question to be explored is whether another event caused unforeseen injuries. What if the bus in our example swerved to avoid a large truck that had crossed the double line and was barreling toward the bus full of innocent passengers? The plaintiffs would be hard-pressed to prove the bus driver was the proximate—natural and direct—cause of personal injuries the plaintiff suffered when the bus hit their car. Liability in this case would likely not rest entirely with the bus driver or company because the unforeseen event of the truck coming across the line also played a role in the extent of the plaintiff’s injuries.
It should be noted that some states use a “substantial factor” test with proximate cause. A substantial factor contributes materially to the event of an injury. A factor—acts or omissions—is substantial when its effects are in operation until the injury happens. Trivial acts or omissions are not considered proximate cause in these states.
How are Experts Involved?
Lawyers often hire experts to help explain that the defendant caused the plaintiff’s injury. As such, an expert would testify as to actual and proximate causation. In the bus accident example, an expert would perform an accident reconstruction analysis to help determine if there were unforeseen events that contributed to the plaintiff’s injuries sustained when the bus hit their car. That expert might be deposed by the opposition and ultimately explain his or her accident analysis in courtroom testimony to help a jury assess causation.
What are Damages?
Once liability—duty and breach—and causation are proven, the court turns to assessing and awarding damages. Actual damages in tort law are intended to compensate plaintiffs for proven harm, loss, or injury. In breach of contract disputes, the purpose of damage awards is to put the injured party in the position they would have been if the defendant had performed under the contract. Courts award punitive damages when a defendant’s actions are extremely reckless or malicious in nature.
How are Experts Involved?
Courts typically rely on expert reports and testimony to calculate damages. An expert may be needed to help determine the amount of wages or income a plaintiff lost due to their injuries. Expert advice also informs award amounts for medical care, rehabilitation, and ongoing costs associated with a personal injury.
In contract disputes, courts often rely on expert assessments of property damage and repair costs. Calculation of stock price drop injuries in securities litigation, for example, typically require experts with in-depth knowledge of financial markets and economics. With the right expertise, attorneys are able to establish these three essential components of a successful case.