What is the test for damages for loss of capacity to earn in a personal injury case?

Personal injury lawsuits almost invariably include claims for damages for loss of past and future earnings which the plaintiff would have earned, had the defendant’s negligence and the resulting injury not occurred. Since Andrews v. Grand & Toy Alberta Ltd., 1978 CanLII 1 (SCC), [1978] 2 S.C.R. 229, it has been acknowledged that, technically speaking, it is not loss of earnings for which compensation is being made but rather it is for loss or impairment of a capital asset, namely, the plaintiff’s capacity to earn income. The courts usually hold the value of a particular plaintiff’s capacity to earn is equivalent to the value of the earnings that she or he would have received, whether in the past or in the future, had the tort not been committed.