Anna J. Schwartz, a research economist who wrote monumental works on American financial history in collaboration with the Nobel laureate Milton Friedman while remaining largely in his shadow, died on Thursday at her home in Manhattan. She was 96.

Her death was confirmed by her daughter Naomi Pasachoff.

Mrs. Schwartz, who earned her Ph.D. in economics at the age of 48 and dispensed policy appraisals well into her 90s, was often called the “high priestess of monetarism,” upholding a school of thought that maintains that the size and turnover of the money supply largely determines the pace of inflation and economic activity.

The Friedman-Schwartz collaboration “A Monetary History of the United States, 1867-1960,” a book of nearly 900 pages published in 1963, is considered a classic. Ben S. Bernanke, the Federal Reserve chairman, called it “the leading and most persuasive explanation of the worst economic disaster in American history.”

The authors concluded that policy failures by the Fed, which largely controls the money supply, were one of the root causes of the Depression.