As in previous editions, three principal objectives guided the writings of this book: first, to explain statistical methods used in business and by economists in the clearest possible way; second, to draw case material from real-world situations in order to demonstrate the practical applications of those methods; third, to surround both theory and cases with an abundance of problems, based on real data whenever possible and graded in level of difficulty. The late Edwin Mansfield was for many years a distinguished professor of economics at the University of Pennsylvania. He was an internationally recognized expert in the economics of technology and industrial organization. His numerous texts, all published by W.W. Norton, have sold millions of copies around the world. In 1979, when Sino-American scientific agreements were finally reached, Mansfield was the first American economist to lecture in the People's Republic of China.