摘要：Objectives. The plaintiffs’ lawyers for a class action suit, which was launched in Quebec on behalf of all patients with lung cancer whose disease was caused by cigarette smoking, asked us to estimate what proportion of lung cancer cases in Quebec, if they hypothetically could be individually evaluated, would satisfy the criterion that it is “more likely than not” that smoking caused the disease. Methods. The novel methodology we developed is based on the dose–response relationship between smoking and lung cancer, for which we use the pack-years as a measure of smoking, and the distribution of pack-years of smoking among cases. Results. We estimated that the amount of smoking required to satisfy the ”more likely than not” criterion is between 3 and 11 pack-years. More than 90% of the Quebec cases satisfied even the most conservative of these thresholds. Conclusions. More than 90% of cases of lung cancer in Quebec are legally attributable to smoking. The methodology enhances the ability to conduct class action suits against the tobacco industry. Legal actions have been launched in different jurisdictions seeking compensation from the tobacco industry for harms done to alleged victims of tobacco-related diseases. If an identified individual launches such an action, that individual has to demonstrate that the tobacco industry shares responsibility for the fact that he or she smoked and that it is more likely than not that smoking caused the disease. As an alternative, a class action may be launched on behalf of an unnamed group of individuals who, collectively, may be claimed to be victims of tobacco-related disease. In this situation, the same components of proof are required. In jurisdictions where there may be thousands or millions of cases of lung cancer, the feasibility of a class action suit is challenged by the requirement to demonstrate that each claimant meets the “more likely than not” criterion. This project was initiated in response to a request to one of the authors to participate as an expert witness in a class action undertaken in the Province of Quebec, Canada, on behalf of people with tobacco-related diseases. In Quebec, the law allows for plaintiffs to request a “collective recovery” against a defendant. The law states: The court orders collective recovery if the evidence produced enables the establishment with sufficient accuracy of the total amount of the claims of the members; it then determines the amount owed by the debtor even if the identity of each of the members or the exact amount of their claims is not established. 1 In such a regime, if the court finds for the plaintiffs and orders a collective recovery, it could authorize individuals seeking redress to make their claims against the collective recovery fund, to a court-appointed administrator, through a procedure that would be simpler and less contentious than a court case. The court would stipulate the conditions that a claimant would have to satisfy to secure a share of the collective recovery fund. We examined the issue of quantifying the number of people on behalf of whom “collective recovery” could be claimed in a class action suit brought by diseased smokers against the tobacco industry. In this article, we do not deal with the issue of tobacco industry responsibility for smoking behaviors, though a suit would clearly need to address this. Nor do we deal with the algorithm that might be used for disbursing money from the collective recovery fund, though a finding for the plaintiffs would clearly need to address this. Finally, we do not deal with the nature of evidence in a case where the state seeks to recover health care costs from the industry.
