Do you want to know why Americans really were angry enough to elect Donald Trump as President?

Well, here it is — from an academic report with the dull title “The Rise and Nature of Alternative Work Arrangements in the United States 1995-2015,” which was researched and written by economics professors from Harvard and Princeton.

Their conclusion: 94 percent of the job growth over the last 10 years occurred in “alternative work arrangements.”

What’s an “alternative work arrangement?” Those are people who aren’t really attached to a particular company. They are freelancers, or temporary workers, or on-call workers and contractors.

According to Professors Alan B. Krueger (Princeton) and Lawrence Katz (Harvard) these alternative jobs now make up 15.8 percent of the workforce compared to just 10.7 percent before the Great Recession of 2008.

Only 0.4 percent of the millions of new jobs — or about 500,000 — were traditional employment arrangements.

Both of these professors are also members of the National Bureau of Economic Research, the organization that decides when there is a recession in the US. So Krueger and Katz are both influential.

Here’s the funny part, if you can laugh at numbers like this. Just a few years ago Krueger served as the assistant secretary for economic policy for the Obama Administration and he was also chief economic for the President’s Council of Economic Advisors.

So, the Democrats shouldn’t have been surprised that jobs and the economy were going to be a major issue in the last election.

As I’ve said again and again, the economy is always very important in presidential elections. But the weakness in the job market made it the most important issue last year despite the fact that the candidates, and the media and the pundits were distracted by a lot of other admittedly entertaining stuff that really wasn’t foremost on voters’ minds.

If you’ve been reading my column you already know most of the problems with the job market. Despite the fact that there are 14 million more jobs now than when President Obama took office, that still isn’t enough to absorb all the people who had lost their jobs and all the people who have since gotten old enough to get a job.

Last Friday, the Labor Department announced that another 156,000 jobs were created. But you can never tell from the government releases whether December’s jobs were quality ones or not.

The 146 million jobs that now exist in the US are only 6.5 million more than existed at the peak of employment in late 2007, before the economy soured.

And the jobs that have been created aren’t as good, so many people have had to hold more than one job to make ends meet. All those multiple job holders mean that someone else is unable to find work.

The first draft of the Krueger/Katz report was finished last March but wasn’t highly publicized. The latest draft, which doesn’t look like the final one, came out on Sept. 13 but only recently was made public.

So the two initial drafts of the professors’ conclusions were available to the Democrats’ inner circle early enough for the Party to have adjusted for the election. But the party didn’t. Nor did it apparently listen to the advice of former President Bill Clinton who was urging his wife, Hillary, to make the economy the main campaign issue.

That’s what he did in 1992 when he won. She ignored the advice and she lost.

The report by Krueger and Katz wasn’t the only warning the Democrats were getting. One prominent Democrat who I met a month or so before the election had been telling people very high up in the Democratic Party that the economy wasn’t as healthy was they believe, or pretending to believe.

I tried to contact Krueger with questions but he didn’t get back to me. The big one is: why have these alternative work arrangements taken over for traditional, full-time jobs?

In their paper the professors seem to put the blame for this shift away from traditional jobs — where a worker is attached to a company that pays benefits, unemployment insurance, etc. — on the worker. “Many possible factors could have contributed to the large increase in the incidence of alternative work arrangements,” the profs write.

One is the “possible increase in demand for flexible hours (perhaps supported by the increased availability of health insurance as a result of the Affordable Care Act) may also have contributed,” they write.

Maybe. But how’s this for a more logical explanation. After the Great Recession companies were afraid to take on the cost of full-time employees so they resorted to freelancers, contract workers, part timers and the like.

Krueger and Katz said that higher paid and older workers are more likely to get caught up in these alternative work arrangements.

And now, nearly 10 years after that frightening time for the American economy companies are still in the habit of not hiring traditional workers or are simply too afraid to do so.

As I suggested in last Thursday’s column, one of the first things on President-elect Trump’s agenda should be to have all the economic data subjected to a full-blown government audited. Until he can dig through the muck of economic data and decide what the job market is really doing he can’t solve this country’s economic problems.

Trump has declared that he will get rid of the ObamaCare, which is the nickname for the Affordable Care Act. Whether he follows through on that pledge or not, he first needs to know how that will affect the 95 percent of workers that Krueger and Katz say recently got jobs with no health or other benefits.