There is a need within the EU for a reference framework for the statistical comparison of data on production, consumption, external trade and transport. To this end, Council Regulation 3696/93 establishes a Classification of Products by Activity (CPA) to ensure compatibility between national and EU classification systems and hence between national and EU statistics. The CPA system consists of six levels of classification, each made up of alphabetical or numerical codes. It shall be employed by the Commission and the Member States for product classifications used for statistics collected after 31 December 1993. A transitional period for adoption of the code by the Member States extends from 1 January 1994 to 31 December 1995. A Statistical Programme Committee (SPC) will assist the Commission in work relating to the CPA, especially with regard its interpretation. It will also advise on the incorporation of amendments, and additions to the code made necessary by technological or economic developments. Subcategories under the "Research and Development Services" Division of the CPA include the groups "Natural Sciences and Engineering" (physical sciences; chemistry and biology; engineering and technology; agricultural sciences; medical sciences and pharmacy; other natural sciences) and "Social Sciences and Humanities" (cultural sciences, sociology and psychology; economics; law; linguistics and languages; social sciences and humanities). A full listing of the CPA is annexed to the Council Regulation.