If Americans were able to match the scores reached in Canada, which ranks seventh on the O.E.C.D. scale, the United States’ gross domestic product would rise by an additional 6.7 percent, a cumulative increase of $10 trillion (after taking inflation into account) by the year 2050, the report estimated.

Robert G. Lynch, an economist who wrote the Washington Center report, explained why he took the trouble to make these what-if calculations.

“One of the main goals was to see how we could promote more widely shared and faster economic growth,” said Mr. Lynch, who teaches economics at Washington College in Chestertown, Md. In the three decades that followed the end of World War II, almost all Americans, no matter where they fell on the earnings scale, enjoyed at least a doubling of their real incomes.

But that balanced growth has evaporated. While those at the top have continued to experience robust income increases, everyone else’s income has either stalled or dropped. The average income of the bottom 20 percent of households sank by more than 8 percent from 1973 to 2013, while the inflation-adjusted incomes of the top 20 percent grew by about 60 percent, according to the report. The top 5 percent enjoyed an 80 percent jump.