The indicators lack detail, have proved difficult to use and interpret, and were often contested when used in OECD Environmental Performance Reviews. In 2014, data on protected areas (broken down by IUCN management categories) were added to the OECD Annual Quality Assurance (AQA) of environmental reference data to enable countries to check and complement the data prefilled from the WDPA and the MDGs. This ad-hoc checking has, however, not been sufficient to produce reliable data.