Canadian Gov't, Exporters Seek to Join CAFC Suit on Cohen's 'd' Test as Amici

The Canadian government and a group of eight Canadian lumber exporters sought to file an amici curiae brief in a case at the U.S. Court of Appeals for the Federal Circuit on the Commerce Department's use of the Cohen's d test to detect "masked" dumping. Filing unopposed for leave to file the briefs on May 28, the parties said they can provide "unique and robust explanations of the Cohen's d denominator, a full understanding of which will" aid the court to settle the issues in the case (Mid Continent Steel & Wire v. United States, Fed. Cir. # 24-1556).

In the case, the Court of International Trade sustained Commerce's use of a simple average of standard deviations in the Cohen's d test denominator in an antidumping duty investigation on steel nails from Taiwan (see 2402120036). The trade court said it couldn't find any fault with Commerce's logic.

In the proposed amici brief, the Canadian parties initially noted that the Cohen's d denominator represents the variance of the groups of data, which are tested for differences using the d test. If the d coefficient is calculated without a denominator that consistently and accurately standardizes mean differences in the numerator, it doesn't provide useful information about the difference between the groups, the brief said.

The statistical literature clearly shows that getting the denominator via simple averaging "is appropriate only if the test and comparison groups are equal in size," the Canadian parties said. Here, Commerce has accepted that the literature doesn't support simple averaging when the data groups are of unequal size. "Nevertheless, Commerce continues to simple average," the brief said.

The agency argued that group size is a proxy for measuring "reliability." In response, the proposed amici said Commerce's claims are "unreasonable, internally inconsistent, and at odds with basic principles of statistics."