UNITED NATIONS — Poverty may be down worldwide, yet that does not mean that yesterday’s poor are today’s middle class. Data analyzed by the Pew Research Center concluded that more than half the world’s population remains “low-income,” while another 15 percent are still what a report issued by the center on Wednesday called “poor.”

The share of the global poor, defined as those who lived on $2 a day or less, fell from 29 percent in 2001. Most of the people in that category, though, took “only a moderate step up the income ladder,” the report concluded: 56 percent were “low-income,” in 2011, living on $2 to $10 a day.

The report defined as “middle” or “upper-middle” income those who lived on $10 to $50 a day. Fewer than one-fourth of the world’s population met that criteria. “Even those newly minted as middle class enjoy a standard of living that is modest by Western norms,” the report said, with barely 16 percent of the world’s population living above the official United States poverty line — $23,021 for a family of four in 2011.

The report echoed some of the findings of the final report of the Millennium Development Goals, issued by the United Nations earlier this week. It said the share of people living in dire poverty — less than $1.25 a day — had fallen by more than half in the quarter century between 1990 and 2015. But the Pew study struck a more sober tone, signaling that those who had escaped poverty are still teetering on the edge of being poor, which is particularly striking in populous countries like India or Bangladesh that have virtually no safety net for those who suddenly fall ill or lose their jobs.