What is a scientist testifying to when a scientist is called into court to testify? His or her opinion on what science can be interpreted as saying on the issue? Or his or personal opinion on the issue?
When a professional from any of the research fields is called to court to give his opinion in his professional capacity, he will be known and treated as an expert by the court. His opinion will be considered as an expert opinion relating to the case. Example: a psychiatric doctor is called to give his opinion concerning to the mental health of an accused in a murder case.