Definition: Superlative indices
Price or quantity indices that are "exact" for a flexible aggregator. A flexible aggregator is a second-order approximation to an arbitrary production, cost, utility or distance function. Exactness implies that a particular index number can be directly derived from a specific flexible aggregator.
Organization for Economic Cooperation and Development (OECD), "Measuring Productivity - OECD Manual: Measurement of Aggregate and Industry-Level Productivity Growth", Paris, 2001