Although the U.S. is on a record streak for job-creation, many Americans still feel like they can't get ahead — it's not their imagination. The last three decades have seen the economy churn out more and more jobs that offer inadequate pay, a group of researchers found.

"The history of private-sector employment in the U.S. over the past three decades is one of overall degradation in the ability of many American jobs to support households — even those with multiple jobholders," they wrote.

The group wants to popularize a new economic metric, called the Job Quality Index, that goes beyond the usual labor market barometers, which tend to focus on the quantity of employment. To be sure, there has always been plenty of jobs that don't pay well. But, as the index's creators found when crafting their measurement, there is now a growing number of low-paying jobs relative to employment with above-average pay.

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"In 1990, the jobs were pretty much evenly divided" said Daniel Alpert, a founder of Westwood Capital and one of the creators of the index. In the process of running the numbers, he said, "We discovered that 63% of all jobs that were created since 1990 were low-wage, low-hour jobs. That was a pretty stunning statistic."

To calculate the index's value, the researchers split up the jobs created every month into those that pay above average and those that pay below average, and then divide one figure into the other. An index value below 100 means there are more lower-paying jobs relative to higher-paying jobs; a value above 100 means the opposite.

Other entities involved in the creation of the index are the Cornell University Law School, the University of Missouri at Kansas City, the Coalition for a Prosperous America and the Global Institute for Sustainable Prosperity.

This month, the index is just over 80, meaning there are 80 high-paying jobs for every 100 low-paying jobs. That's a stark drop from 1990, when there were 94 high-paying jobs for every 100 low-paying jobs.

"There aren't enough 'good jobs' to go around," the Brookings Institution proclaimed earlier this month, when it released a report that found 44% of all workers are low-wage workers. These workers make a median pay of just $18,000 a year.

Looking at the job landscape this way shows an aspect that isn't demonstrated by the headline numbers often touted by the press and the White House — such as the unemployment rate, which is near a 50-year low, or the number of job openings, which has been higher than the number of unemployed people for a year and a half.

"Academia is trying to make sense of all these conflicting signals, you have a very tight unemployment rate but low labor force participation relative to prior cycles, low levels of wage growth, and everyone scratching their head and saying, 'How is this so?' " Alpert explained.

He hopes that academics, as well as investors and policy makers, become a regular audience for the index. If it had existed in 2018, he said, "the Fed would not have made the mistake of raising interest rates."

Going forward, the index will be updated and released on the same day the Bureau of Labor Statistics releases monthly jobs figures, Alpert said.

"It's a grain of salt with which to digest the meal that's served up by the BLS every month."