Robert Dow Buzzell Sr., 71, a marketing professor at three universities and a leading authority on the economics of marketing and advertising, died Nov. 6 of complications of amyotrophic lateral sclerosis, or Lou Gehrig's disease, at Capital Hospice in Arlington. He lived in Alexandria.

Dr. Buzzell, who grew up in Arlington, gained his greatest distinction at Harvard Business School, where he taught from 1961 to 1993 and held the Sebastian S. Kresge chair in marketing. He wrote 11 books and hundreds of papers, was an expert witness on marketing strategy and patent infringement and served on the boards of several companies. From 1993 to 1998, he was a professor of marketing at George Mason University. He was a distinguished lecturer at Georgetown University from 1998 to 2000.

"Bob's research, writing and teaching influenced the scholarly community, the teaching community and the business community in many ways," Stephen A. Greyser, an emeritus professor at Harvard Business School, said in a statement. "His influence and stature in the fields of both marketing and strategy were extraordinary."

Dr. Buzzell emphasized pragmatic approaches to business that could be verified through empirical research. He did not believe that simplified, one-size-fits-all solutions were effective management tools.

He may have been best known for designing a research program in the mid-1970s called Profit Impact of Marketing Strategies, which analyzed the profits of individual businesses. Conducting field studies at numerous companies, Dr. Buzzell was among the first to show that companies with large market shares lose their dominance gradually unless they invest continually in innovation and the development of products.

In 1987, Dr. Buzzell published "The PIMS Principles: Linking Strategy to Performance," and his research led to the founding of the Strategic Planning Institute, a business research organization. Among his other books, "Marketing in an Electronic Age" (1985) examined the effect of new technologies on marketing, and a 1990 book co-written with John A. Quelch, "The Marketing Challenges of Europe 1992," explored the economic impact of the emerging European Union.

From 1968 to 1972, Dr. Buzzell was executive director of the Marketing Science Institute, a nonprofit research organization at Harvard, and was chairman of the Harvard Business School marketing faculty from 1972 to 1977.

Dr. Buzzell, who was born in Lincoln, Neb., moved to Arlington as a boy and graduated from Washington-Lee High School in 1949. He graduated from George Washington University in 1953 and was elected to Phi Beta Kappa. He received a master's degree in business from the University of Illinois in 1954 and a doctorate in business in 1957 from Ohio State University. He taught at Ohio State before joining the faculty at Harvard.

He held visiting professorships at the University of Virginia and at the European Institute of Business Administration in France. He was on the boards of directors of VF Corp., Harleysville Mutual Insurance, Lane Bryant, Hills Department Stores, Sherwin Williams, Friendly Ice Cream and General Nutrition Corp.

After living in Wellesley, Mass., for 30 years, Dr. Buzzell moved to Alexandria in 1993. He was a member of Little River United Church of Christ in Annandale.

Survivors include his wife of 51 years, Edith Moser Buzzell of Alexandria; four children, Susan Browning and Barbara Schwartz, both of Alexandria, Robert D. Buzzell Jr. of Fairfax Station and William Buzzell of Perrysburg, Ohio; and nine grandchildren.

Robert D. Buzzell Sr. taught at George Mason University after 32 years at Harvard Business School.