Academic advocates of gun control apparently need to manipulate the data in order to argue for background checks on private gun transfers. Even the prestigious medical journal, the Lancet, does not seem to be above publishing junk science on gun control. There has been extensive, glowing media coverage from the Los Angeles Times, CNN, Reuters, and US News & World Report.

Currently, background checks must be performed when a gun is purchased from a dealer. “Expanded” background check laws would require that checks also be conducted on private transfers of guns (say between a father and a son or with a neighbor).

These laws exist in 19 states. Of course, previous public health researchers simultaneously carefully pick one state at a time to examine (Missouri or Connecticut), which years to look at, and what types of crime to study. To do the matter justice, a researcher really must look at all of the states that passed the laws, and then compare the changes in crime rates between those states that passed the laws to those that didn’t.

Using data from 2010, the new Lancet study claims that these background checks on private transfers will reduce state firearms deaths (homicides plus suicides) by 57 percent. Yet, few researchers would look at firearm deaths across states in one year.

To put this in perspective, let’s look at another simplistic comparison. A lot of people like to point to the UK’s lower homicide rate and fewer guns and attribute this to strict gun control laws. Many cite this as proof that gun control reduces homicides. But there is a problem. The UK had an even lower homicide rate before the country banned handguns. After the ban, homicide rates rose by 50 percent over for the next 8 years.

The point is that homicide or suicide rates can differ for lots of reasons that have nothing to do with gun control, and that simply looking across countries or states is often quite misleading.

The most accurate option is to see how a place’s crime rates change after new laws go into effect and then compare that change with the changes that occurred in places where the laws didn’t change.

Again, the cherry-picking of numbers is outrageous. Gun laws for 2009 are used to evaluate firearms deaths in 2010. Then 2013 is chosen as the year that firearm ownership is looked at. No explanation is offered for why these different years are used. The normal approach is to use all the available years of crime or suicide data. One must have a very good reason for omitting certain years data, and there really is no good explanation for what was done in the Lancet study.

There are many other problems with this study, such as looking at the impact of the different gun control laws in separate regressions instead of studying their impacts all at one time.

When I did my own study in the 2010 edition of "More Guns, Less Crime" (University of Chicago Press), I used data for all the states from 1977 to 2005. I found that these expanded background checks were associated with a very small and statistically insignificant 2 percent increase in murder rates.

Expanded background checks have become this year’s hot political issue for Democrats. After every mass shooting, President Obama has called for these new checks. Strangely, the recent shootings in Oregon, Colorado, California, and Paris are being used to push gun-control laws that already existed in those places and that evidently failed to prevent the attacks. There’s already evidence that these attacks don’t decline in frequency as a result of expanded background checks.

Public health research has become completely corrupt. Too often, the conclusions seem to be more important than the accuracy of the research. With money flooding in from Michael Bloomberg, George Soros, and others, we are unfortunately going to be seeing a lot more of these types of studies in just the coming year.