By at least one measure, inequality among working men has grown for decades. But, in 2015, it accelerated: The wage gap among men saw its largest single-year increase on record.

Top earners — men who made more than 95 percent of their peers — saw wages last year rise by 9.9 percent, according to an analysis of federal data. Men in the middle — with earnings higher than half their peers — saw a much-smaller 2.6 percent increase.

While that gap between male earners in the 95th and 50th percentiles saw its biggest rise, last year’s increase only extended a long-running trend.

“It is the most, but to say that inequality hasn’t been growing for the last 35 years would be wrong,” said Elise Gould, an economist with the left-leaning Economic Policy Institute who conducted the analysis earlier this month, as part of a larger report on wage inequality.