(CNN) The company that makes the annual Best Colleges rankings said that the University of Oklahoma gave "inflated" data on its alumni giving rates for two decades.

U.S. News & World Report, which produces the coveted Best Colleges rankings, said Oklahoma would be listed as unranked in its 2019 edition because of the false data, which stretched back to 1999.

For the 2019 Best Colleges rankings, the university originally said its two-year alumni giving rate was 14% but later informed U.S. News that the correct number is 9.7%, the magazine said.

The false data affected Oklahoma's placement in the national universities, best value schools, top public schools, best colleges for veterans and A-plus schools for B students rankings and lists, U.S. News said.

The rankings are based largely on data provided by the universities, such as graduation rates, class sizes and standardized test scores of students. Alumni giving rates make up 5% of the rankings formula because "giving measures student satisfaction and post-graduate engagement," U.S. News writes in its methodology