More than 40 percent of America’s homeless population are people with disabilities and the number appears to be rising, according to an annual report on homelessness from the Department of Housing and Urban Development (HUD).

In 2008, 42.8 percent of all adults using homeless shelters had a disability compared to 37.1 percent in 2007. The report calls this increase “unusually large for a single-year change.” The numbers could reflect an increased need or simply better data collection, the report says.

Meanwhile, just 17.7 percent of the general adult population reports having a disability meaning that a significantly larger percentage of people with disabilities are homeless compared to the rest of the population.

One reason for the high number of homeless people with disabilities may be that people in this population are more likely to be impoverished than those without disabilities, according to the report. Moreover, reliance on relatively small Supplemental Security Income (SSI) payments — which average 44 percent below the federal poverty level — could also make it difficult for people to retain permanent housing.