President Obama might want to brush up on his facts before hosting next week's critical summit on "violent extremism." By claiming "99.9% of Muslims" are moderate and reject the radical tenets practiced by the Islamic State, he grossly underestimates the threat, including in America.

"The overwhelming majority of Muslims reject that interpretation of Islam," he recently told CNN's Fareed Zakaria. "It's very important for us to align ourselves with the 99.9% of Muslims who are looking for the same thing we're looking for — order, peace, prosperity.

While his remarks echo his earlier State of the Union speech, in which he said "the vast majority" of Muslims share Western values, this was the first time he has quantified the "extremist" threat. In his mind, only 0.1% of the world's 1.6 billion Muslims hold radical beliefs.

But taking into account scientific measurements of attitudes in the Muslim world, his estimate is foolishly low. For example, several recent Pew Research Center polls of Muslims in Muslim countries — as well as in America — show strong support for many of the extremist notions that Obama assumes they shun.

An alarming 26% of American Muslims ages 18 to 29 believe suicide bombings vs. non-Muslims "can be justified." That means our Muslim youth are just as radicalized as their counterparts in France, Germany and Britain.

"The higher levels of support for suicide bombing seen among young American Muslims resembles patterns found among Muslims in Europe," Pew said.

The respected polling agency also found in a separate 2013 poll that vast majorities of Muslims abroad "clearly support" barbaric forms of Islamic punishment, including: stoning women accused of cheating on their husbands, chopping off the hands of thieves and robbers, publicly whipping people who "insult" Islam, and beheading those who convert to another religion.

"Taking the life of those who abandon Islam is most widely supported in Egypt (86%) and Jordan (82%)" — two Muslim nations viewed as fairly moderate — Pew found in its 2013 survey.

Foreign Muslims favor making the harsh Islamic legal code known as Shariah — the same one implemented by the Islamic State — the "law of the land" for Muslims and non-Muslims. Only, they prefer appointing "religious judges" to enforce it.

Overwhelmingly, they condemn homosexuality while supporting polygamy.

Large pluralities even favor "honor killing" daughters who engage in premarital sex.

Most troubling: Solid majorities in Egypt, Lebanon and several other Muslim nations agree that carrying out suicide bombings against non-Muslims "can be justified," according to another Pew survey of Muslim attitudes on terrorism conducted last spring.

The beliefs of Muslims in America aren't exactly enlightened in comparison.

Though Pew's seminal 2007 poll of 1,050 U.S. Muslims did not ask about Shariah law, it found that even in America, a large majority of Muslims — 69% — believe women should be separated from or subordinated to men.

What's more, a majority of devout Muslims here don't think Muslims should adopt "American customs." They think the Muslim community should remain distinct from American society, and they frown on other Muslim immigrants assimilating into American life.

Younger Muslims express even less patriotism, with 60% under 30 saying they're more loyal to Islam than America.

By overwhelming margins, American Muslims say they've opposed the war on terrorism from the start. Almost two-thirds of all U.S.-born Muslims (65%) think using force in Afghanistan was wrong, an opinion wildly at odds with the general public, 61% of whom supported military strikes there after 9/11.

And a solid majority (55%) of all U.S. Muslims don't think America is fighting a just war against terrorism. Almost half doubt the 9/11 attacks were even carried out by Muslims, making American Muslims the biggest "truthers" in the country.

In light of these findings, it's grossly misleading to say our Muslims are dramatically more assimilated than their European counterparts. It only serves to blind Americans to the growing internal threat.

Before Wednesday's White House summit, our commander in chief ought to do some independent research before making unrealistic assessments about the religious motivations of terrorists. His false assumptions give the enemy political cover while lowering the guard of the American public.

Next: Why radical Muslims are good Muslims.

• Sperry, formerly IBD Washington bureau chief, is author of "Infiltration: How Muslim Spies and Subversives Have Penetrated Washington."