Since the recession, many measurements of the U.S. economy improved: The stock market rallied, unemployment fell and the number of Americans worried about getting enough food began to drop.

Yet for all that, one important measure has lagged.

The proportion of people over 60 deemed to be “facing hunger” – based on their answers to a U.S. Census survey – has been on a steady climb that began in 2001 and has plateaued but not dropped in recent years, according to a report released Wednesday.

For another year, “there was no significant decline in seniors ‘facing hunger,'” said James P. Ziliak, economics professor and director of the Center for Poverty Research at the University of Kentucky, who co-authored the report. “This rate has been stubbornly stuck.”

It is one of the curiosities of the recession that the recovery has not done more to alleviate food insecurity and hunger.

The rates of food insecurity among the general population, which likewise rose during the recession, began to drop after 2011. But despite the economic recovery, they remain above pre-recession levels, according to the USDA’s most recent annual report on the subject.

But it is among Americans older than 60 that the recovery’s effects appear to be weakest, according to figures in the new report, which was released by Feeding Hunger, a nonprofit group, in partnership with the National Foundation to End Senior Hunger. It was written by Ziliak and Craig Gundersen of the University of Illinois.

To determine how many people face troubles finding food, the Census survey asks a battery of 18 questions such as whether respondents had skipped meals or cut the size of portions for lack of money. Respondents who answered six or more of the questions in the affirmative were deemed to be “facing hunger.”

In 2001, 610,000 people over age 60, or about 1.4 percent, were deemed to be facing hunger. But since then, the rate climbed, jumping with the recession, and then continued to climb until plateauing in recent years. In 2015, the last year in the analysis, 2.1 million people over age 60 were facing hunger, or about 3.1 percent.

Over 14 years, in other words, the proportion of older people facing hunger has doubled.

It’s not clear why. Ziliak speculated that several phenomena could be at work. Maybe it’s that older Americans have had a harder time recovering from the drops in wealth that came with the housing downturn. Or the low interest rates they earn on their savings. Or rising rents.

“Unfortunately, I don’t have any hard evidence to give you a smoking gun,” Ziliak said.

Others have blamed the rising hunger rate on gaps in programs to feed older people.

“After lifetimes of hard work many of America’s seniors are put in the terrible of position of having to choose between groceries and medical care,” said Feeding America CEO Diana Aviv.

A 2015 report from the U.S. Government Accountability Office, for example, found that “many older adults with low incomes who likely need meals do not receive them.”

As food and transportation costs have risen, “federal funding is failing to keep pace with the need,” said Erika Kelly, government affairs officer at Meals on Wheels America.

As a result, since 2005, the number of meals that the Meal on Wheels network has served has dropped by 23 million annually.

“One in four of our programs have a waiting list with an average of 200 individuals,” Kelly said.