What is the relevant case law for giving evidence from a third party witness in a personal injury case?

Second, the weight to be afforded the testimony of other witnesses – who frequently are asked to relate evidence about observations over a long period of time – must be carefully scrutinized to exclude simple assumptions, opinion or facts related by one of the interested parties. Katarynych J. gave little weight to such evidence in Stulberg v. Batler, supra, and required the affiants to have actual opportunity for observation of the parties’ interactions, rejected mere opinion without a factual basis and would not accept what a witness had simply been told by the applicant.