The fourth basic concept involves Witnesses. Lay witnesses (MRE/FRE 601, 602, 701) must satisfy the Competency requirement (personal knowledge and ability to communicate). The rules make a clear preference for facts, not opinions.
Expert Witnesses (MRE/FRE 702, 703) must demonstrate special knowledge or training that will actually help. This usually involves a showing in three areas:
1. Assisting trier of fact
2. Qualifications
3. Standard for admissibility of theory or technique ((a) Frye: general acceptance in particular field; or b) Daubert: evidentiary reliability & scientific validity [(i) can it be tested? has it been tested? has it been subjected to peer review and publication? what is the known or potential rate of error? is it generally accepted by the relevant scientific community?])