Legal Definitions - opinion testimony

Opinion testimony refers to a witness's statement of belief, inference, or conclusion, rather than a direct observation of fact. While witnesses are generally expected to testify about what they personally saw, heard, or did, there are specific circumstances where courts permit them to offer an opinion. This type of testimony is typically allowed when it is based on the witness's rational perception and helps the court or jury understand the evidence or determine a fact in issue.

There are two main types:

• Lay Opinion Testimony: Offered by an ordinary witness based on their everyday experiences and perceptions. It must be something that a reasonable person could infer from their observations and be helpful to understanding their testimony.
• Expert Opinion Testimony: Offered by a witness who possesses specialized knowledge, skill, experience, training, or education in a particular field. This type of opinion is allowed when the subject matter is beyond the common understanding of the average person and the expert's specialized knowledge would assist the court or jury in understanding the evidence or determining a fact.

Here are some examples illustrating opinion testimony:

• Example 1 (Lay Opinion):

  During a trial concerning a bar fight, a bystander testifies, "The man in the red shirt looked extremely agitated and aggressive right before he threw the punch."

  Explanation: This is opinion testimony because the witness did not measure the man's emotional state with a device but rather formed an inference based on their perception of his demeanor and actions. While not a precise factual measurement, a layperson can reasonably interpret and describe another person's emotional state based on observation, and this opinion helps the jury understand the context of the altercation.

• Example 2 (Expert Opinion - Medical):

  In a medical malpractice case, a neurosurgeon testifies, "Based on the MRI scans and the patient's symptoms, it is my professional opinion that the delay in surgery directly led to the permanent nerve damage."

  Explanation: This is expert opinion testimony. The neurosurgeon, as an expert in their field, is offering a professional judgment about the causation of the patient's injury. This opinion is based on specialized medical knowledge, diagnostic tools, and experience, which is beyond the common understanding of a layperson, and helps the jury determine the impact of the alleged malpractice.

• Example 3 (Expert Opinion - Forensic):

  During a criminal trial for a hit-and-run, an accident reconstruction expert testifies, "After analyzing the skid marks, vehicle damage, and debris field, it is my conclusion that the defendant's vehicle was traveling at least 60 miles per hour in a 35-mile-per-hour zone at the moment of impact."

  Explanation: This is expert opinion testimony. The accident reconstruction expert, with specialized training in physics and accident dynamics, is providing an inference about the speed of the vehicle. This opinion is based on technical analysis and expertise that would not be available to an ordinary witness and is crucial for the jury to understand the circumstances and severity of the collision.