Widows have historically been one of the nation's most financially vulnerable demographic groups, but in recent decades they have grown more resilient and less likely to fall into poverty, a new study says.

The average poverty rate of the nation's widows fell from 20 percent in 1994 to 13 percent in 2014, according to a new study by the Center for Retirement Research at Boston College.

The chief reason cited for the decrease was the increasing education levels and workforce participation among married women—a trend that the study says will continue and lead to the poverty rate of widows dropping to 8 percent by 2029.

"Among earlier generations, women tended to be homemakers while their husbands were the breadwinners, making wives financially dependent on their husband's income," the report stated. "Upon a husband's death, the widows saw their Social Security benefits decline and their pensions reduced or lost completely."

The center's researchers stressed that this still happens, and is the reason widows remain twice as likely as married women to fall into poverty. But they noted that, as a group, women are facing less financial distress upon the death of a husband because they are better prepared to be financially independent.

The report noted, for example, that less than 10 percent of women born before the 1930s held a college degree. Among women born in 1950, however, 25 percent held college degrees.

The study, which looked at Social Security Administration earnings and benefit data, also found that the average number of years U.S. widows have been in the labor force has gone from 15 in 1994 to 25 in 2014, with the number projected to increase to 32 in 2029.

"Simultaneously, each younger birth cohort of women has shown higher labor force participation at any given age," the report stated. "Now that women work more, they are less reliant on their husbands' income in retirement."

To a lesser extent, the drop in widow poverty rates can also be attributed to the fact that the population of married women is on average more educated, primarily because less educated women are marrying less. "The pool of women who eventually become widows has become better-educated, which likely reduces the risk of falling into poverty," the report said.