The right of contribution exists among parties who are considered joint tortfeasors. The term "joint tortfeasors" means that two or more persons are jointly or severally liable under negligence law for the same injury to persons or property [injury to property], whether or not judgment or payment has been recovered [recover, to] from all of them". When there is such a disproportion of fault among joint tortfeasors as to render inequitable an equal distribution among them of the common liability by contribution, the relative degrees of fault of the joint tortfeasors shall be considered in determining their pro rata shares. In making this determination, you shall consider both the nature of the conduct of each party at fault and the extent of the causal relation between that conduct and the damages [damage] suffered.