The lack of a clear definition of various sexual assault terms within the federal government is making it impossible to determine just how often rape, sexual assault and other gradations of these events are occurring, according to a federal watchdog.

The Government Accountability Office reported Thursday that four federal agencies in particular run at least 10 different programs aimed at collecting data on sexual violence. But GAO said these efforts use 23 different terms to describe these acts of violence, and said the agencies don't have common definitions for these terms.

"For example, the same act of sexual violence could be categorized by one data collection effort as 'rape,' whereas it could be categorized by other efforts as 'assault-sexual' or 'nonconsensual sexual acts,' among other terms," GAO said.

The agency said the Departments of Defense, Education, Health and Human Services and Justice use several different terms in their data collection efforts.

It also said federal agencies don't publish any description of how they determine which actions are rapes, sexual assault or lesser-degree events like nonconsensual sexual acts.

"Publicly available measurement information could enhance the clarity and transparency of sexual violence data," GAO said.

GAO added that the confusion makes it difficult to say with any precision how often these events occur.

"For example, in 2011 (the most recent year of available data), estimates ranged from 244,190 rape or sexual assault victimizations to 1,929,000 victims of rape or attempted rape," GAO said. "These differences can lead to confusion for the public."

GAO recommended that the Office of Management and Budget create a process to help harmonize federal data on sexual violence. But the agency indicated that OMB was not yet willing to take that step.

"OMB stated that convening a forum may not be the most effective use of resources at this time, in part because the data collection efforts are not far enough along in their research," GAO said. "However, OMB said it will consider convening or sharing information across agencies in the future."

The report was requested by Sen. Claire McCaskill, D-Mo., and sent to her in a July letter and publicly released Thursday. In its letter, GAO outlined the various data collection activities of the four federal agencies, and created a chart showing the inconsistencies with which agencies use some terms, but not others, when describing sexual violence.