A bulldozer backed into P and crushed his leg. J.I. (D) manufactured the bulldozer and sold it to Harold D. Smith & Sons, Inc. (Smith (D)); Smith (D) sold it to P's employer, who used it on the construction site where P was working. P sued Ds for strict liability and negligence. Causation was a major issue, and the parties focused on the bulldozer's lack of a backup alarm and P's failure to notice the vehicle's approach. P sought to admit evidence that, after the accident, P's employer installed a backup alarm on the bulldozer that injured him and that, in 1987, Case (D) made backup alarms standard equipment on all 450C bulldozers which has previously been optional. The trial court largely excluded this evidence, citing Rule 407. The jury returned special verdicts for Ds. P appealed on a number of evidentiary issues including: (1) admission of evidence that P received workers' compensation benefits; (2) exclusion of lay opinion testimony; (3) exclusion of expert opinion testimony; (4) exclusion of evidence of subsequent modifications; and (5) exclusion of P's requested jury instruction on the defense of 'plaintiff's misconduct.'