What is the test for reducing a defendant’s liability for damages for depression and anxiety?

Where a plaintiff suffered from a malady before sustaining a compensable injury, or where the evidence shows that there is a measurable risk that a plaintiff’s pre-existing condition will become symptomatic, the court must decrease the defendant’s liability for damages to account for the pre-existing condition: Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458. In this case, the plaintiff’s depression and anxiety were active shortly before the accident. I find it likely that, even if the accident had not happened, the plaintiff would have continued to suffer from a degree of depression and anxiety for some years to come. I find that because those conditions were not disabling before the accident, there was no measurable risk that they would have disabled the plaintiff absent the accident. They would, however, have required medication and the plaintiff would have benefited from some psychological counselling for depression and anxiety.