Adding a layer of depth and authority to arguments, expert opinions are informed perspectives or conclusions provided by individuals who possess specialized knowledge, skills, or experience in a particular field. They are often used to bolster claims in persuasive writing and can provide valuable support for counterarguments. By integrating them effectively, writers can create a persuasive argument that appeals to both logic and authority.
In forming an opinion, experts may consider their own experience, knowledge, or education but they are generally expected to base it on research evidence, from studies ranging from uncontrolled case series to randomized controlled clinical trials. As with other forms of evidence, expert opinions can be biased (Leskinen et al., 2003).
For experts to offer unbiased opinions, they should be aware of the limitations of their own perspective and knowledge. As a result, they are usually required to present all information that was presented to them before forming an opinion. However, a trial court rule states that “facts or data on which an expert’s opinion is based which are not otherwise admissible need not be excluded where experts in the subject matter would reasonably rely upon them.”
This rules, known as Rule 705, allows expert witnesses to rely on three possible sources of information in forming their opinions. The first source, personal observation, reflects existing practice. It is a common technique for medical experts, for example. However, expert witness testimony based on personal observation is still considered inadmissible in many courts.
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