In 1923, Arthur C. Nielsen opened a statistical consulting firm in Chicago. During the 1930s, he added a service that provided radio ratings, which allowed advertisers to estimate the size of the audiences of particular stations and programs. The company soon introduced machines that recorded consumers' selection of radio and television programs; for many years, Nielsen dominated the market for television ratings information, much of which came from some 1,200 of these machines placed in homes around the country. By the middle of the 1960s, the company's annual revenues were about $60 million, and it employed nearly 7,000 people around the country. At the end of the 1970s, when Nielsen had begun to use computers to analyze large quantities of retail-sales data, the company had become the nation's leading market-research firm, with $400 million in annual sales and 17,000 employees nationwide. Between 1984 and 1996, the company was a division of the Dun & Bradstreet Corp. of New York City. At the turn of the century, the descendant of Arthur Nielsen's small Chicago firm was a worldwide marketing information company with 21,000 employees in 100 countries. ACNielsen Corp.'s American headquarters were still located in the Chicago area, in Schaumburg.

This entry is part of the Encyclopedia's Dictionary of Leading Chicago Businesses (1820-2000) that was prepared by Mark R. Wilson, with additional contributions from Stephen R. Porter and Janice L. Reiff.