In Bomersheim v. Los Angeles Gay and Lesbian Center, ___ Cal.App.4th ___ (May 26, 2010), the Court of Appeal (Second Appellate District, Division One) reversed an order denying class certification of a negligence claim against a medical clinic that gave a group of patients the wrong treatment.
The opinion has an interesting discussion of classwide "causation":
Slip op. at 12-13. The causation discussion cites Occidental Land, Vasquez, and Massachusetts Mutual.
An inference of causation arises when a material event impacts an individual whose subsequent actions constitute a reasonable response. In the class context, where individuals are uniformly subjected to a material stimulus and thereafter uniformly act in a manner consistent with a reasonable response, a classwide inference is raised that the stimulus caused the response.
Here, putative class members all came to the Center seeking treatment for syphilis, a potentially life-threatening disease. They were given the wrong medication. After being informed that the treatment may have been ineffective, they sought retreatment. A reasonable inference as to the entire class is that the initial mistreatment caused members to seek retreatment. Causation can therefore be presumed on common proof.