In a recent speech at the Federal Reserve Bank of Boston, Federal Reserve Chair Janet Yellen discussed the issue of income and wealth inequality, noting that the past few decades have caused a rift between the have and have-nots that may be the largest in our nation's history. From 1989 to 2013, income for the top 5% of earners grew by 38%, while the rest of the population saw gains of less than 10%.

There are many reasons for this disparity in wealth, not the least of which was the economic crisis that followed the housing crash. As far as income is concerned, I think the biggest contributor to the yawning gap between rich and poor is the current state of job creation. Simply put, most of the jobs available these days are clustered toward the low end of the wage spectrum.

An ongoing problem, spurred to new heights since 2008
Yellen is right that the gap between high and low earners has been widening for decades. Since 1979, the median usual weekly earnings hasn't changed much at all, and wage stagnation means that the average pay workers take home today doesn't buy any more than it did back then.

The financial crisis decimated the job market, and expanded the chasm between the rich and the poor. A large number of high-wage jobs were lost, in addition to middle-wage jobs that paid between $14 and $21 per hour. While those job groups haven't yet recovered, low-wage jobs are coming back strong.

How strong? A study done for the U.S. Conference of Mayors this past summer noted that the jobs in higher- and middle-wage sectors where losses were greatest -- like manufacturing and construction -- yielded average annual salaries of approximately $62,000 in 2008 and 2009. By comparison, the jobs that were added to the economy by the second quarter of 2014 produced annual incomes of just over $47,000.

How can the situation still be so dire, when unemployment is down to 5.9%, and the economy generated a hearty 248,000 jobs in September? A perusal of the most recent jobs report from the Bureau of Labor Statistics explains just where the job growth has come from so far this year.

With the exception of construction, the sectors that have added at least 230,000 jobs in 2014 have been primarily leisure and hospitality, in addition to the retail trade. These are the very segments that the National Employment Law Project reported were gaining jobs more quickly than high- and middle-wage jobs earlier this year.

After the 2001 recession, higher-wage jobs led the rebound, at 8% growth, with low-wage close behind, at 7.9%. This time, the least lucrative jobs have grown by 10.3%, compared with growth in high-wage occupations of 7.4%. Though middle-wage jobs are rebounding at a faster clip than they did in 2001, this segment also experienced the biggest losses during the Great Recession.  

Unfortunately, job projection research by BLS indicates that this trend may continue through the year 2022, at least. The fastest-growing sectors -- which are predicted to make up more than half of all new jobs -- will be those that require only a high school diploma, or less. Those occupational segments encompassed almost two-thirds of all workers in 2012 -- and paid a measly median wage of $27,670 per year. 

Since workers with little discretionary income are not apt to spend, save for retirement, or invest, this prediction doesn't bode well for an economy that hasn't yet recovered from the financial crisis. If the jobs picture doesn't change, perhaps it never will.

Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.