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Why does Trump keep saying that the murder rate is the highest in 45 years?

Donald Trump speaks at a campaign event in Charlotte, North Carolina, U.S., October 26 2016. (REUTERS/Carlo Allegri)

During his celebratory event in North Carolina on Tuesday night, Donald Trump came very close to getting crime statistics right.

"On crime, the murder rate has experienced its largest increase in 45 years," Trump told the crowd. "We are going to support the incredible men and women of law enforcement, and we are going to bring this terrible crime wave to an end. Highest in 45 years, the murder rate."

Increases in crime have been part of Trump's campaign pitch for months. Well before the FBI released compiled statistics for 2015, Trump asserted that crime was getting out of hand; once those data were released, Trump latched on to them. Our fact-checkers have been over this before, granting Trump a four-Pinocchio rating for the above claim. But let's flesh it out again.

It is true that the percentage increase in number of murders from 2014 to 2015 was the highest in 45 years. The number of murders jumped by 10.2 percent over that period, the highest jump since 1971, when the number of murders went up by 11.1 percent.

But the increase in the number of murders was only the largest since 1990. There were 1,447 more murders in 2015 than in 2014. Between 1989 and 1990, the figure increased by 1,938. At the time, that was only a 9 percent increase in the number of murders, because there were a lot more murders. In terms of the actual number of murders, 2015 saw the highest figure since ... 2008.

None of this, mind you, is the murder rate. The murder rate is a figure that's tied to population, calculating the number of people murdered out of every 100,000 residents of the United States. That's important because 24,703 murders in 1991 was out of a population of 253 million. It would be like having 31,200 murders in 2015 -- about twice the rate we actually saw. In fact, it was precisely twice the rate.

The murder percentage increase in the murder rate in 2015 matched that of 1979 -- going back 36 years. The actual rate, though, was exceeded in 2009, within the presidency of Barack Obama.

That long-term decline is important. Americans constantly think that crime is going up, according to data from Gallup, but in reality it's gone down fairly consistently over the last two decades.

2015 was an exception, and the question is whether or not that exception will continue. Solving the murder problem in Chicago would go a long way to fixing the problem; the number of murders in that city in 2015 equaled one-third of the increase in murders from 2014 to 2015.

So why does Trump keep citing an inaccurate figure? There are a few possibilities. One is that he's confusing the numbers, which, to be fair, are confusing. Another is that he's intentionally inflating the perception of increasing crime because it's central to his political positions.

That he's using the percentage increase in the number of murders instead of the number of murders or the murder rate hints that his motivation is the second of those two options. After all, a big reason that the number of murders increased at such a big percentage is that the number of murders had dropped so much! Adding 1,400 murders to 14,200 yields a much bigger percentage increase than adding the same count to 24,700, which is the figure America saw at its peak.

An increase in murder is bad, unequivocally. But it's simple to talk about the numbers behind that accurately and pointedly.

If you want to.