As a business litigation attorney I often need to prove lost profits as an element of damages.  Generally, witnesses called to testify at trial are not allowed to give opinions.  Their testimony is limited to facts based upon their first hand knowledge and not opinions or conclusions.  The exception is when an expert  witness is called to testify on a subject to assist the jury in understanding a particular issue.

A person is qualified to testify as an expert if he has special knowledge, skill, experience, training, or education sufficient to qualify him as an expert on the subject to which his testimony relates.  When calling an expert witness I will set out his or her qualifications on a particular subject, ask the expert what his or her assignment was in the case, how he went about performing his or her assignment, what opinions were formed and the basis for each opinion.

From my experience when both sides call competent expert witnesses with opposite opinions, the juries do not always decide the case based upon the expert’s testimony but on their feeling of which party is more deserving.