Grounds of opinion, when relevant

If a living person's opinion is relevant, the facts, observations or tests that form the basis of that opinion are also admissible. This applies not just to experts but to any witness whose opinion matters. The consequence is the court can examine the underlying grounds (experiments, data, observations) along with the opinion itself.

Meera, a forensic analyst, testifies that a paint sample matches a suspect's car. Under this rule she must also describe the experiments, tests and observations she relied on to form that opinion. The court will consider both her conclusion and the underlying results.