When liberal nanny-staters infringe on their citizens' freedom to enjoy anything from soft drinks to semi-automatics, they often flatter themselves as being science-based technocrats. But look into the science behind these government intrusions and you'll find little to no evidence justifying the power grabs.

New York City Mayor Michael Bloomberg gets the "technocrat" label in the media (Time magazine referred to his "technocratic, data-driven governing style"), and liberal outlets have touted his various impositions on New Yorkers' lives as "backed by science." But the preponderance of data does not support his mandates on gun control, size of sodas, and calorie counts.

Bloomberg is spending millions of his own dollars lobbying for a federal ban on "assault weapons." The bill is plainly a political exercise not tied to actually preventing gun deaths.

First, such bans rest on a meaningless definition of "assault weapon." Under the bill Bloomberg supports, California Sen. Dianne Feinstein's Assault Weapons Ban of 2013, a rifle can become an illegal assault weapon simply by having a threaded barrel -- meaning you could put a silencer or flash suppressor on it -- or a detachable stock.

After laying out its arbitrary definition of "assault weapon," Bloomberg's favorite bill proceeds to name dozens of specific guns, while exempting others. The dividing line between banned and permitted is, at best, an aesthetic one: Does it look too militaristic?

The 10-year ban on assault weapons passed by Congress in 1994 had no measurable effect. "We cannot clearly credit the ban with any of the nation's recent drop in gun violence," concluded one 2004 study by the University of Pennsylvania. As liberal Washington Post blogger Brad Plumer put it, "One reason is that assault weapons were never a huge factor in gun violence to begin with."

Yet this is where "technocrat" Bloomberg is throwing his money.

Bloomberg's war on soda is similarly not rooted in science, despite claims to the contrary.

After a judge struck down Bloomberg's rules restricting large sodas, the liberal Center for American Progress headlined an article "Bloomberg's Supersize Soda Ban Rejected By Judge, But Backed By Science." That article makes a true point: Drinking soda isn't a healthy habit. But where's the evidence that banning sodas larger than 16 ounces from certain food establishments would have a positive effect on health?

First, consider the loopholes. CAP illustrates its article on the ban with pictures of 7-Eleven Big Gulps. But Bloomberg omitted convenience stores, including 7-Eleven, from his ban on big sodas. Maybe Bloomberg technocratically knows that sodas are healthy when paired with Buffalo Chicken Go-Go Taquitos?

The propaganda arm of Bloomberg's anti-soda crusade included a claim that a soda a day "can make you ten pounds fatter a year." Bloomberg's health commissioner approved these ads, the New York Times reported, despite a warning by the city's chief nutritionist: "As we get into this exacting science, the idea of a sugary drink becoming fat is absurd."

Bloomberg's "data-driven approach" to banning soda involves silly numbers games. After the court ruling voiding the ban (and calling it "capricious"), Bloomberg fired back that "Five thousand people will die of obesity this year in New York. The best science tells us that sugary drinks are a cause of obesity."

Bloomberg also likes to cite a study by a Harvard University postdoctorate fellow estimating how many people die from sugary drinks. That author concluded "about one in every 100 deaths from obesity-related diseases is caused by drinking sugary beverages." Multiply those purported 5,000 obesity-related deaths by the 1-in-100 number from Harvard and you get 50 soda-related deaths in New York City. Subway trains killed more people in NYC last year. More people were murdered in Brooklyn's Crown Heights alone.

To prevent all those 50 soda deaths, Bloomberg would have to totally ban soda and hope those New Yorkers don't take up non-banned sweet drinks like chocolate milk -- although a Centers for Disease Control and Prevention study suggests that's exactly what people do when faced with soda constraints.

Another Bloomberg mandate -- that the city's fast-food restaurants post calorie counts on their menus -- has met with mixed results in academic studies. One study actually found "some evidence that males ordered more calories when labels were present," as an article in the journal "Health Affairs" described it.

Mayor Bloomberg probably has his citizens' best interests at heart when he uses the law to control their lives. Too bad he doesn't have the best data at hand.

Timothy P. Carney, The Washington Examiner's senior political columnist, can be contacted at tcarney@washingtonexaminer.com. His column appears Monday and Thursday, and his stories and blog posts appear on washingtonexaminer.com.