Class definitions can be extremely difficult for plaintiffs. In addition to holding that merits-based class definitions cannot support certification, courts have begun to hold that some definitions are simply too broad. Overbroad definitions usually are symptomatic of other problems with the proposed class.

Want an example? Take the case of Kemblesville HHMO Center LLC v. Landhope Realty Co., 2011, U.S. Dist. LEXIS 83324 (E.D. Pa. Jul. 28, 2011). Kemblesville concerns the dispersion of methyl tertiary-butyl ether (MTBE), a gasoline additive that helps reduce harmful automobile emissions, but which can contaminate groundwater under the wrong circumstances.

In Kemblesville, the plaintiffs sued based on a theory that the presence of MTBE in a few sites surrounding a gas station diminished the value of property out to a 2,500-foot (roughly, half-mile) radius. (They referred to this as the "stigma class," because the reduced property values would come from the stigma of being located near the contamination.) The plaintiffs asked the court to certify a class of all property owners within that radius.

The court began by noting the burden plaintiff carries in arguing for certification, and the fact that "[t]he requirements set out in Rule 23 are not mere pleading rules."  It also articulated why overly broad class definitions are not a good idea.

"The class must be sufficiently identifiable without being overly broad. Overbroad class descriptions violate the definiteness requirement because they include individuals who are without standing to maintain the action on their own behalf."

(Emphasis added, internal citations and quotation omitted.) The plaintiffs tried to avoid any overbreadth by claiming that the relationship between the alleged contamination and the geographic boundary of their class was a "merits issue." (This was an extremely odd choice. A number of courts have held that a class definition is fatally flawed if it requires a determination on the merits to decide who is in the class. While technically, the only merits question here was whether the plaintiffs' "objective" definition was reasonable, invoking the specter of a merits inquiry still seems self-defeating.) Nevertheless, the court disagreed.:

Plaintiffs' proposed class includes properties simply because they exist, irrespective of any actual connection to Defendants' activities. The Court does not at this stage require Plaintiffs to adduce definitive evidence about the specific amount and effect of MTBE dispersion. However, to enable this Court to conclude that there is a reasonable relationship between the relevant MTBE release and the proposed class area, Plaintiffs need to adduce some evidence of dispersion that indicates MTBE may have traveled, or will ever travel, near a radius of 2,500 feet.

Finally, the court also found a numerosity problem that stemmed from the overbreadth of the class.

However, because this class definition is too overbroad, I cannot accept Plaintiffs' numerosity argument. Plaintiffs have failed to provide evidence that MTBE contamination is present throughout the class area.

According to Plaintiffs, many properties are in contaminated or soon-to-be contaminated areas. However, that estimate is purely speculative, and conclusory allegations do not satisfy Rule 23(a)(1)'s numerosity requirement.

(Emphasis added.)  So what can defense lawyers take from this ruling? Don't be afraid to challenge an overly broad class definition. Even if it looks "objective," if a class sweeps too many potential members in, determining who is actually entitled to relief will require individualized inquiries. That is not merely a problem with predominance or commonality; it can also be a problem with the definition itself.