We previously discussed the case of Dr. Smith, the pathologist whose errors have wrongfully convicted many.

The defence that Dr. Smith relied upon was that it was an honest error in judgement. There is no liability for error in judgement under tort law.

Establishing the standard of care is first examined by looking at what a reasonable person would do in all the same circumstances of the case [in the same profession, of course].

In Stewart v. Pettie, [1995] 1 S.C.R. 131 the Supreme Court said,

The “reasonable person” of negligence law was described by Laidlaw J.A. in this way in Arland v. Taylor, [1955] O.R. 131 (C.A.), at p. 142:

He is not an extraordinary or unusual creature; he is not superhuman; he is not required to display the highest skill of which anyone is capable; he is not a genius who can perform uncommon feats, nor is he possessed of unusual powers of foresight. He is a person of normal intelligence who makes prudence a guide to his conduct. He does nothing that a prudent man would not do and does not omit to do anything a prudent man would do. He acts in accord with general and approved practice. His conduct is guided by considerations which ordinarily regulate the conduct of human affairs. His conduct is the standard “adopted in the community by persons of ordinary intelligence and prudence.”

Four hypothetical factors are then examined:

1. Probability of injury arising from defendant’s conduct
2. Likelihood of severity of injury
3. Balanced against cost of avoiding risk
4. And social utility of defendant’s conduct

The first two variables are usually weighed more than the last two variables.

Finally, based on specific facts of case with 4 factor test, the court evaluates if the defendant breached standard of care by trier of fact.

Learned Hand Formula

Another way of expressing the calculation is the Learned Hand Formula.

In US. v. Carroll Towing Co. 159 F.2d 169, Judge Learned Hand expressed a formula previously created in T.J. Hooper 60 F.2d 737 (2d Cir.):

B < p × L

Negligence in this calculation is determined when the Burden (B) is less than the Probability (P) of harm, multiplied by the degree of Loss (L).

But the formula is not a strictly accurate mathematical calcution, and courts continue to apply context to cases.