More households are at risk of having inadequate income in retirement as measured by an index used by the Federal Reserve, according to an analysis by the Center for Retirement Research at Boston College.

The index takes into account projected retirement income—from savings, pension income and other sources—as a percentage of working income and the replacement rate that will be needed. Households whose projected replacement rates are at least 10 percent below the need are considered to be "at risk."

For all income groups, that figure stood at 53 percent in 2010 compared with 44 percent in 2007, the study said. Broken down by income levels, the report said that the rate rose for the lowest-income third from 54 to 61 percent, for the middle third from 43 to 54 percent and for the highest third from 35 to 44 percent.

Similar results were found when breaking down by age groups, with the oldest group studied, those 50-59, experiencing the greatest increase in retirement risk, 12 percentage points to 44 percent.

Major contributing factors included investment losses during that period, the increase in the Social Security age at which fill benefits can be drawn, the decline in housing values—affecting potential for income from taking out a reverse mortgage—and the decline in returns on the type of fixed-income investments favored by retirees.