How much evidence will be required by a plaintiff to prove their case on the issue of causation?

12 Snell v. Farrell was a case in which medical negligence was alleged, and the issue raised was concerned with the difficulties facing a lay plaintiff in such a case in meeting the onus of proof on the issue of causation. It would in my view be wrong to apply the observation of Lord Mansfield there cited so as to require that plaintiffs prove their case by the most compelling evidence which they could be expected to adduce, because the result would not only be to increase the length and cost of litigation but to introduce into the process a new element of uncertainty, for a plaintiff would never know how much further the evidence had to go beyond establishing the case on the balance of probabilities. The question in Snell v. Farrell was how little evidence would suffice for a plaintiff in the circumstances of that case to meet the initial onus on the issue of causation; here the issue is whether the plaintiff need prove more than would normally be necessary to establish a case on the preponderance of probabilities.