Patricia McKnew Nielsen, 83, a Chicago civic and cultural activist who grew up in Washington and whose husband devised TV's Nielsen ratings, died of lung cancer July 16 at her home in Winnetka, Ill.

Mrs. Nielsen was born in the District and graduated from the Madeira School. Inspired by the ideals of first lady Eleanor Roosevelt, she was determined to get an education and devote her life to public service, but her father disapproved of Roosevelt's influence and refused to pay for college. She instead won a scholarship to Bryn Mawr College, where she graduated magna cum laude in 1943 with a bachelor's degree in psychology.

During World War II, she worked with other Bryn Mawr students who were given an assignment by the military to help crack German and Japanese codes. She also worked as a psychologist at Johns Hopkins School of Medicine, where she helped design experiments on the psychological determinants of nutrition and taste and, as her husband recalled, tended to the laboratory rats. As a psychologist with the State Advisory Service of the Social Security Board in 1943-44, she designed aptitude tests for prospective employees.

After her marriage in 1944 to Arthur C. Nielsen Jr., a young Army engineer and statistician, she moved to Winnetka, where her husband joined his father's A.C. Nielsen Co. Under the younger Nielsen's leadership, the company became the world's largest market research company.

Mrs. Nielsen devoted her time and energy to her family and extensive volunteer work.

Her mother had done pioneering work in Washington with Margaret Sanger, founder of the organization that became the Planned Parenthood Federation of America, and family planning became a lifelong cause for Mrs. Nielsen as well. She was a trustee of Planned Parenthood for 44 years and Chicago-area president of the organization from 1973 to 1975. She also worked on family planning and related issues worldwide with the Center for Growth Alternatives and the Population Institute.

In 1971, she became a trustee of the village of Winnetka; later, she was a trustee of New Trier Township. She was chairman of the Illinois Human Relations Commission from 1975 to 1980 and worked closely with Whitney M. Young Jr., who was executive director of the National Urban League.

A champion of education, she was a trustee of the Chicago Educational Television Association and a supporter of the University of Chicago, Northwestern University and Bryn Mawr College. She also served on the board of Northland College, a liberal arts institution with an emphasis on environmental studies in Ashland, Wis.

From 1991 until her death, she was a trustee of the Gamaliel Foundation, an organization that helps lower-income residents become advocates for their neighborhoods. She also was an intrepid traveler, visiting such disparate places as Antarctica and the jungles of New Guinea.

In addition to her husband of 61 years, of Winnetka, survivors include three children, Dr. Arthur C. Nielsen III of Winnetka, J. Christopher Nielsen of New Orleans and Elizabeth Nielsen Cocciarelli of Florence; a sister, Susan Caskin, and a brother, Dr. Donald H. McKnew Jr., both of Washington; and seven grandchildren.

Patricia McKnew Nielsen's husband created TV's Nielsen ratings.