What are experts allowed to give opinions on in a court case?

In court cases, experts are permitted to provide opinions on hypos and ultimate issues, which refers to hypothetical scenarios that illustrate potential outcomes based on their expertise as well as direct opinions on the key issues at stake in the case. Ultimate issues are those that are directly related to the matters that the jury must ultimately decide, such as whether a defendant had the mental capacity to commit a crime or whether certain actions met the standard of care in a negligence case. The purpose of allowing experts to weigh in on these issues is to support the jury’s understanding and guide them in making informed decisions based on expert knowledge that is beyond the average juror's understanding.

By contrast, general behavior and lifestyle choices may not be within the scope of specialized knowledge and could be seen as common knowledge rather than expert testimony. Private thoughts of a defendant are typically considered inadmissible unless a party introduces them, as they fall outside objective analysis that an expert would provide. Emotional appeals to the jury would not be appropriate for experts, as their role is to deliver impartial, fact-based analysis rather than sway emotions.