Is Environmental Litigation Rising or Falling? It Depends on Which Database You Ask

Commercial legal databases show environmental litigation rising sharply over four decades. The federal government’s own case records show it declining over the same period. Both are real data. The difference is not measurement error. It reflects how each database was built, what it was designed to capture, and what it systematically leaves out.

A new paper I co-authored with Christopher Rea (Brown University) and Jennifer Kagan (University of Hawai’i at Mānoa), published this week in Interest Groups & Advocacy, examines six major U.S. federal litigation data sources. We find that source choice shapes basic conclusions about litigation trends, the types of cases counted, and who sues whom.

The Database Problem

Federal litigation research draws on a small set of sources. Commercial databases like Westlaw and NexisUni index written judicial opinions. The Federal Judicial Center’s Integrated Database (FJC IDB) is built from administrative records filed with the courts. PACER is the federal court system’s public document repository. CourtListener, run by the Free Law Project, is an open-access alternative that draws on all three.

Each source was built for a different purpose. Each makes different tradeoffs between comprehensiveness, searchability, and cost. Those tradeoffs are not neutral. They determine which cases appear, which disappear, and what the resulting data can and cannot support.

We use environmental law as our test case because it is a domain where litigation genuinely matters. Government agencies rely on civil suits to enforce the Clean Air Act and the Clean Water Act. Nonprofit organizations sue those same agencies when they fail to enforce the law. Who files suits, against whom, and under which statutes reflects the balance of power in environmental politics. Getting the data right is not incidental to that inquiry. It is the inquiry.

The Same Trend Runs in Opposite Directions

The starkest finding is the simplest. Commercial, document-based sources like NexisUni show environmental litigation rising steadily since the 1970s. The FJC IDB, which covers every civil case filed in federal district court, shows it declining since the 1990s.

The apparent growth in NexisUni is largely an artifact of the database’s own expansion. After Congress mandated free availability of all federal court opinions in 2002, NexisUni added millions of previously excluded documents. More opinions in the database registers as more litigation. The underlying filing rate did not change. The FJC IDB, tracking actual case filings rather than published opinions, captures what happened in the courts, not what happened in the database.

This has direct implications for policy arguments. Claims that NEPA litigation is hampering federal permitting or that the courts have become the primary arena for environmental obstruction rest on trends drawn from document-based sources. Those trends reflect database construction more than legal reality.

A Third of Environmental Cases Are Mislabeled

The FJC IDB categorizes civil cases using administrative codes called Nature of Suit (NOS) codes. Researchers studying environmental litigation typically filter for cases coded “Environmental Matters.” We find that this filter misses roughly a third of substantively environmental conflicts.

Those cases are not peripheral. Environmental justice organizations routinely frame lawsuits as civil rights claims. Challenges to federal agency decisions under NEPA and the Clean Water Act often land under codes like “Administrative Procedure Act” or “Real Property.” Parties make strategic choices about how to frame a case, and those choices do not map cleanly onto the administrative categories that researchers use to find them.

A sample built on “Environmental Matters” cases alone understates the scale of environmental conflict and systematically excludes the civil rights framing at the center of environmental justice advocacy. The mismeasurement is not random. It is structured by the same legal and political dynamics the research is trying to understand.

Who Sues Whom Depends on Where You Look

The third finding concerns litigants. Across all sources, the six most prominent plaintiff-defendant pairings account for roughly two-thirds of environmental cases. But the relative prevalence of those pairings shifts substantially depending on the source.

NexisUni overrepresents cases in which environmental nonprofits sue the federal government. A researcher relying on it would conclude that organized advocacy groups challenging federal agencies drive environmental legal conflict. The FJC IDB tells a different story, one in which government enforcement against private firms is more prominent. Both pictures are empirically grounded. They describe different parts of the same legal landscape. The choice of source determines which part the researcher sees.

These are not minor analytical differences. They bear directly on questions central to interest group scholarship: which organizations are most active in court, what strategies they pursue, and how legal conflict relates to policy outcomes. Source selection shapes those conclusions before any analysis begins.

Four Lessons for Researchers

We offer four practical lessons. First, no single source is adequate. Document-based and metadata-based sources move in opposite directions on basic trend questions. Triangulating across both is necessary.

Second, NOS codes cannot define a research sample on their own. Cross-validating with statute-based keyword searches captures cases that the administrative classification misses.

Third, linking case metadata to court documents produces the most complete picture. The FJC IDB covers the universe of filings; judicial opinions supply the substantive legal content. Together they support analyses that neither source can sustain alone.

Fourth, sharing cleaned datasets and documented construction protocols makes the field’s data infrastructure cumulative and correctable. The biases we identify are not inherent to legal research. They are artifacts of specific data choices, and specific data choices can be changed.

The ultimate payoff is not methodological precision for its own sake. It is a more accurate empirical foundation for understanding how advocacy unfolds in the courts, who wins, and what that means for policy. In a period when litigation is invoked constantly as a problem to be solved or a tool to be wielded, the data underlying those arguments deserves the same scrutiny we apply to the arguments themselves.

Rea, C.M., Kagan, J.A., and Katz, J. (2026). “Breaking down barriers to litigation and judicial advocacy research: a comparison of legal data sources.” Interest Groups & Advocacy. https://doi.org/10.1057/s41309-026-00262-4