There are roughly 9 million lesbian, gay, bisexual and transgender adults living in the U.S. but more concrete data on the number of LGBT Americans is needed to help shape public policies, according a report released today by the Williams Institute.

The report, titled "How Many People Are Lesbian, Gay, Bisexual and Transgender?" finds that a good estimate of the number of LGBT Americans — adults — is about 9 million, or roughly the population of New Jersey. The approximate population of the U.S. is more than 311 million people (including children), according to the most recent data from the U.S. Census Bureau.

The report from the Williams Institute, a national think tank located at the UCLA School of Law,  also estimates that people who report "same-sex sexual behavior" in their lifetime is as high as 19 million Americans, or 8.2 percent — and this is about the population of Florida. Some 11 percent, or nearly 25.6 million Americans, say they "at least have some same-sex attraction" — or more than the population of Texas.

9 million LGBT people living in U.S. according to national report

Key findings of the report include:

• About 3.5 percent of adults in the United States identify as lesbian, gay or bisexual and an estimated 0.3 percent are transgender.

• “Among adults who identify LGB, bisexuals comprise a slight majority (1.8 percent compared to 1.7 percent who identify as lesbian or gay).”

• Women are “substantially more likely than men” to identify as bisexual. “Bisexuals comprise more than half of the lesbian and bisexual population among women in eight of the nine surveys considered in the report. Conversely, gay men comprise substantially more than half of gay and bisexual men in seven of the nine surveys,” the report states.

It is crucial to continue to gather data about LGBT people to better understand the population, especially when it comes to shaping public policy, the report states.

“Understanding the size of the LGBT population is a critical first step to informing a host of public policy and research topics,” writes the report’s author, Gary Gates.

“The surveys highlighted in this report demonstrate the viability of sexual orientation and gender identity questions on large national population-based surveys. Adding these questions to more national, state and local data resources is critical to developing research that enables a better understanding of the understudied LGBT community.”

The Williams Institute report comes on the heels of a groundbreaking report issued last week by the Institute of Medicine  urging the federal government to include LGBT questions on federally funded surveys for a better snapshot of the health needs for this specific population.

“Last week, the Institute of Medicine at the National Academies released an analysis of LGBT health research calling for federal statistical agencies to quickly move toward LGBT inclusion in their data collection,” Gates said in a statement.

“The surveys highlighted in this report demonstrate the usefulness of sexual orientation and gender identity questions on large-scale national population-based surveys. Better data can provide the building blocks for critical information to understand the lives of the 9 million LGBT Americans who have been historically marginalized in both society and research,” Gates added.

But what about the 10 percent figure — that 1 out of every 10 people is gay?

Gates told the Washington Post the figure comes from an Alfred Kinsey study of male prisoners in 1948.

“The number stuck,” Gates told the Washington Post. “Here we are, decades later, and it’s still the most prominent number cited.”

The Williams Institute report also points out that determining the size of the LGBT population in the U.S. is challenging due to different survey methods, who is actually included in the LGBT population as well as “a lack of consistent questions asked in a particular survey over time.”

Finding ways to get accurate information about the LGBT population is critical, according to the Williams Institute report.

“The surveys highlighted in this report demonstrate the viability of sexual orientation and gender identity questions on large-scale national population-based surveys,” according to the report.

“States and municipal governments are often testing grounds for the implementation of new LGBT-related public policies or can be directly affected by national-level policies. Adding sexual orientation and gender identity questions to national data sources that can provide local-level estimates and to state and municipal surveys is critical to assessing the potential efficacy and impact of such policies.”

Data for the Williams Institute was compiled from four recent national and two state-level population based surveys conducted between 2004-2009.

The Williams Institute, which focuses on research based on sexual orientation as a way to gain equality, has had its work cited in numerous court cases and policy reports, including the Prop 8 trial and by the Obama administration in its fight to repeal “Don’t Ask, Don’t Tell.”

The Williams Institute is celebrating its 10th anniversary and in a Huffington Post article posted on Wednesday, Chuck Williams, who founded the Williams Institute, said objective research is the key to making change.

“You don’t get laws passed or court cases won by just saying it would be nice or it should be or its not right if you don’t change this. You don’t win that way,” said Chuck Williams, the businessman and academic who founded the namesake institute. “You win by presenting objective data.”

Social conservatives, however, believe the Williams Institute does nothing more than conduct research and release reports to advance the so-called “gay agenda.”

“The Williams Institute, with its generic-sounding name and academic affiliation, seeks to give the impression that it is an unbiased source of information regarding issues of sexual orientation,” said Peter Sprigg in the HuffPo story. Sprigg is senior fellow for policy studies at the anti-gay Family Research Council. “In truth, it is nothing but an advocacy organization, using its resources to promote elements of the pro-homosexual political agenda.”

Joe Solmonese, executive director of HRC, discounted Sprigg’s comments.

“It wouldn’t serve any purpose if their research weren’t objective,” he said. “From where I sit, it’s been incredibly helpful to have factually based, methodologically sound research to back up the cause.”