Question: Choose the single best answer to complete the statement, “A class-action lawsuit …”

A. Is a legal cause of action for a wrongful act perpetrated by a class of wrongdoers.

B. Requires prior certification by a judge before it can go forward.

C. Is appropriate where the claims of a few injured victims can be joined together against a common wrongdoer.

D. Fulfills twin criteria of numerosity and commonality.

E. Can only be filed where there are substantial monetary damages at issue.

Answer: B. A class-action lawsuit describes a legal cause of action where a representative plaintiff(s), known as the lead plaintiff, asserts claims on behalf of a large class of similarly injured members, who then give up their rights to pursue an individual lawsuit. Class-action suits are distinguished from the usual lawsuit, which characteristically affects only one or a few plaintiffs.

Four prerequisites govern an action before it can be deemed a class action: numerosity, commonality, typicality, and adequacy. These are words of art, with specific definitions.

Numerosity denotes a large class membership, usually exceeding 30-40, and sometimes numbering in the thousands, such that the usual joining together of a few injured plaintiffs is not practical. Commonality speaks to common questions of fact and law, typicality requires the claim(s) of the representative plaintiff to match that of the class members, and adequacy demands that the representation of the class members be adequate.

These rules, as well as other important technicalities governing class action, are enumerated in the Federal Rules of Civil Procedure under Rule 23.1 2 Wal-Mart Stores, Inc. v. Dukes et al ., where Wal-Mart was alleged to have violated Title VII of the Civil Rights Act of 1964 by having disparate wages and promotion reflecting gender discrimination.3 The plaintiffs sought an injunction against the alleged practice, as well as monetary damages. An earlier ruling of the U.S. Court of Appeals for the Ninth Circuit gave the green light to this sprawling nationwide class action.

It had started out with Betty Dukes and five other women employees, but grew to more than 1.5 million female Wal-Mart employees. However, on appeal, the U.S. Supreme Court reversed, holding that the certification of the plaintiff class was not consistent with Rule 23(a), as the prerequisite of commonality was not fulfilled. The Supreme Court also disallowed the claim for monetary relief, as it was not incidental or secondary to the injunction sought.

Class-action suits are commonly encountered in mass torts, where a product or accident causes injury to numerous individuals. Other situations include environmental pollution, securities fraud, and improper employment practices.

A favorite target is in the health care industry, where manufacturers of drugs and medical devices face allegations that defective products have been allowed to enter the market, causing harm to end users.

An example is the silicon breast implant litigation of the 1990s. The Food and Drug Administration had placed breast implants in the category of medical products and learned that the Dow Corning Corporation, which manufactured the silicon implants, had withheld safety information. The FDA severely restricted the use of these implants, which predictably led to widespread litigation with billions of dollars of judgment awards and settlements.4 5 and the FDA subsequently required the revision of the package insert of Lipitor and other statins to warn of this association. In 2013, a large Canadian study confirmed the increased incidence of new-onset diabetes in patients taking atorvastatin (hazard ratio, 1.22) or simvastatin.6

However, the outcome of the trial may turn on whether the clear health benefit of lowering serum cholesterol outweighs any purported safety concern.

A fast-growing trend is the filing of class-action suits against nursing homes for providing inadequate care. This is not unexpected, because large numbers of nursing home residents have a common concern over any breach of safety, hygiene, or other statutorily mandated standards of nursing home care. This important topic will be taken up in a subsequent column.


1. Available at .

2. Mullenix LS. Ending class actions as we know them: rethinking the American class action. Emory Law J. 2014;64:399-449 .

3. Wal-Mart Stores, Inc. v. Dukes et al. 131 S. Ct. 2541 (2011) .

4. Snyder JW. Silicon breast implants. Can emerging medical, legal and scientific concepts be reconciled? J. Leg. Med. 1997;18:133-220 .

5. Sattar N, et al. Statins and risk of incident diabetes: a collaborative meta-analysis of randomised statin trials. Lancet 2010;375:735-42 .

6. Carter AC, et al. Risk of incident diabetes among patients treated with statins: population based study. BMJ 2013;346:f2610 .

Dr. Tan is emeritus professor of medicine and former adjunct professor of law at the University of Hawaii, and currently directs the St. Francis International Center for Healthcare Ethics in Honolulu. This article is meant to be educational and does not constitute medical, ethical, or legal advice. Some of the articles in this series are adapted from the author’s 2006 book, “Medical Malpractice: Understanding the Law, Managing the Risk,” and his 2012 Halsbury treatise, “Medical Negligence and Professional Misconduct.” For additional information, readers may contact the author at