Historical 2018 ISORA Data. The International Survey on Revenue Administration (ISORA) collects tax administration data from national or federal tax administrations. In 2018 data was collected on tax administrations' operations and other characteristics in Fiscal Years 2016 and 2017 using common questions and definitions agreed by four international organizations: the Inter-American Center of Tax Administrations (CIAT); the International Monetary Fund (IMF); the Intra-European Organisation of Tax Administrations (IOTA); and the Organisation for Economic Co-operation and Development (OECD). These four Parties signed a Memorandum of Understanding (MOU) governing the administration and management of this worldwide survey. The Asian Development Bank (ADB) assisted with the collection of data.