A well publicized report this week that an estimated 1.5 million American children experienced homelessness in 2005-06 did not use the federal definition of homelessness. Instead, it used a different definition that grossly inflated the actual number.

The report — released Tuesday by the National Center on Family Homelessness and reported by numerous news organizations, including FOXNews.com — estimated that one out of every 50 children in America experienced "homelessness" during that two-year span.

But rather than using the definition of homelessness established by the U.S. Department of Housing and Urban Development, the Massachusetts-based organization used a standard adopted by the Department of Education that includes children who are "doubled up," or children who share housing with other persons due to economic hardship or similar reason.

The difference? About 1,170,000 children.

An estimated 330,000 sheltered and unsheltered homeless children were identified in HUD's July 2007 report to Congress as those who are "literally homeless," or those living in homeless facilities or in places not meant for human habitation, according to the report.

The remaining 1.17 million — those who are precariously housed or who may be doubled up with friends and relatives or paying extremely high proportions of their resources for rent — are not included in HUD's report.

"It's not consistent with the definition that we've applied in academic research for more than 20 years and it's inconsistent with federal housing policy," University of Pennsylvania Professor of Sociology Dennis Culhane, a principal investigator of HUD's report, told FOXNews.com. "People who are doubled up are not counted as homeless."

Culhane — who testified before Congress last year on the reauthorization of the McKinney-Vento Act of 1987, a law that provides federal money for homeless shelters — said the Department of Education uses a different definition to address the needs of temporarily displaced children. The act also requires that states provide "homeless" children access to free public education.

"For that purpose they are labeled 'homeless,' and covered under federal policy to assure that they get transported to their school, but they are not otherwise considered homeless under federal housing policy," Culhane wrote to FOXNews.com.

National Center on Family Homelessness President Ellen Bassuk acknowledged that HUD's "more strict" definition refers to individuals who are "literally homeless," but she said that definition excludes about 30 percent of homeless families housed in private, faith-based or domestic violence-related shelters.

"It's a tighter one," Bassuk said, comparing HUD'S definition of homeless to the Education Department's. "It's not about the absolute fact of literal homelessness versus not … That's the intention of the [DOE] definition and that's why we adopted it."

Bassuk said the number of homeless children in the center's 2005-06 report represents an "extreme undercount" of current figures due to the worsening recession and housing crisis.

"We do not use the numbers for any kind of dramatic effect," Bassuk said. "Our numbers are at best an undercount."

Gregg Wiggins, a spokesman for the Education Department, said its definition of homelessness was changed in the early 1990s to add those who are "doubled up" and unaccompanied youth.

"It made sense for providing school services," said Wiggins.

Patrick Markee, a senior policy analyst for the Coalition of the Homeless, acknowledged the ongoing debate regarding the definition of homelessness, but he said he supported the report.

"Folks who are living doubled-up with another primary tenant are effectively homeless," Markee said. "They may not be sleeping on the sidewalk or on the subway train, but they're homeless."

According to the report, which also graded every U.S. state on how it addresses "homelessness," a staggering 204,053 children in Louisiana were homeless at some point in 2005-06, a figure the report acknowledges may be unusually high due to Hurricane Katrina and Hurricane Rita.

Using the Education Department's definition, that would include students who stayed with relatives as the torrential hurricanes pulverized southeastern U.S. cities.

"People in substandard, overcrowded, or unaffordable housing are facing real housing problems, to be sure, but we won't solve their problems by dubbing them 'homeless' and trying to make them eligible for the minimal resources in the homeless system," Culhane told FOXNews.com in an e-mail.