1. Published by the Institute for Scientific Information, Philadelphia, Pennsylvania, U.S.A.
2. UNESCO Yearbook 1974, Paris, UNESCO, 1975, p. 624 ff.
3. Statistical Abstract of Latin America, Los Angeles, Latin American Research Centre, 1974, p. 43.
4. Yearbook of Nordic Statistics 1974, Stockholm, The Nordic Council, 1975, p. 208.
5. Reference 2,op. cit.,UNESCO Yearbook 1974, Paris, UNESCO, 1975, p. 784 ff.