Americans out of work more than six months have barely benefited from the longest decline in the country’s unemployment rate since 1994.

While the jobless rate dropped for the fourth consecutive month in March, the number of people going more than six months without work rose to 6.12 million. That’s more than four times the average since 1970, according to data compiled by the Labor Department.

Those who exceeded the six-month threshold account for only 13 percent of the drop in unemployment since December, when the rate started shrinking. Their number fell by 206,000 as people out of work for shorter periods tumbled by 1.36 million.

The disparity represents “a persistent source of concern” as unemployment eases, says Robert V. DiClemente, Citigroup Inc.’s chief U.S. economist.

Joblessness has decreased by a full percentage point during the four-month streak. March’s rate dipped to 8.8 percent, the lowest in two years, as the economy added 216,000 workers. The increase in employment was the biggest since May, when census-related hiring swelled the total.