"standardized" education dollars into New York City dollars. With respect to the first factor, Standard & Poor's made a set of calculations using four different academic achievement standards for identifying a successful school district, and again the parties agree, and the referees found, that satisfaction of the Regents Criteria provides an appropriate standard for measuring a successful school. Nor is there any dispute as to the fourth factorthe proper conversion of state education dollars into New York City [*17]dollars. Inasmuch as the purchasing power of a dollar varies across the state, and the successful schools method examined all of the school districts in the state, Standard & Poor's offered two alternative regional cost adjustment indices to determine the cost in New York City dollars: (1) the "New York Regional Cost Index," provided by the State Education Department; and (2) the "Geographic Cost of Education Index" (GCEI), provided by the National Center for Education Statistics.{**8 NY3d at 39} The referees found, and the parties agree, that use of the GCEI was appropriate.[FN4] The differencea huge dollar differencecenters on the second and third factors: the proper weighting adjustments for special needs students, and the use of a 50% cost reduction filter. A. The Low-Income Weighting A successful schools analysis produces "base expenditures," which are estimated costs per pupil. However, such base expenditures must then be multiplied by "weightings" for students with special needs, who require such costly accommodations as differentiated curricula, smaller class sizes, assistive technology and classroom aides. Standard & Poor's assigned a weighting of 2.1 to students with disabilities (special-education students); 1.35 to economically disadvantaged students; and 1.2 to students with limited English proficiency. Although the parties and referees agree that the special-education and English-language weightings were appropriate, the record reflects that the 1.35 low-income weighting applied by Standard & Poor'saccording to which $1.35 must be allocated to students in poverty for every dollar spent on a student not in povertywas irrational and cannot be sustained. Defendants' principal rationale for choosing this weightinga choice that drew considerable criticism from the witnesses and amiciwas that the Standard & Poor's study had identified 1.35 as the proper adjustment for educating economically disadvantaged students. But Standard & Poor's had in fact emphasized that 1.35 was simply a figure that it had "drawn from a review of research literature on the coefficients that education agencies tend to use in practice," and that "insufficient empirical evidence exists in New York to determine how much additional funding is actually needed for different categories of students with special needs to consistently perform at intended achievement levels" (Standard & Poor's School Evaluation Services, Resource Adequacy Study for the New York State{**8 NY3d at 40} Commission on Education Reform, at 8-9 [2004]).[FN5] As a result, Standard & Poor's made clear that its study "does not explicitly recommend a particular set of weightings." (Id.)