Amazon employs over half a million workers. In the past year alone, the online retailer has added roughly a quarter of a million employees to its headcount, and 238 cities across the country are competing to become the location of Amazon's second headquarters, which is estimated to create 50,000 more Amazon jobs.

But according to Dave Edwards and Helen Edwards at Quartz, Amazon may be killing more jobs than it creates. Quartz found that there are 170,000 fewer retail jobs in Amazon-related industries — like bookstores, grocery stores and clothing stores — in 2017 than the year before.

According to their calculations, even if Amazon maintains an impressive 43 percent personnel growth for another year, the total number of workers employed in Amazon-related industries would still decrease by 24,000.

So where are the jobs going? Quartz suggests that an increase in robotic workers could be to blame. They estimate that Amazon added 75,000 new robots to their workforce in 2017 for a total of roughly 100,000. By these approximations, machines constitute 20 percent of all Amazon "employees."

More robots don't always mean fewer jobs, but it may in the case of Amazon. Edwards and Edwards write, "While it may be difficult to prove causality, it's not difficult to see the correlation between a decline of 24,000 human employees and an increase of 75,000 robot employees."

Amazon attests that the investment in technological workers has improved efficiency. CNBC reports it takes 90 minutes on average for a human Amazon employee to find a product and package it, but with the help of robots, a product can be found and packaged in as little as 13 minutes.

This efficiency is one reason why investors are so excited about Amazon. Even though the S&P Retail Index has remained relatively flat in 2017, Amazon's stock is up 57 percent.

CNBC's Jim Cramer says that growth like this is going to lead Amazon to continue to invest in robotics and artificial intelligence in the coming year. "They're going to have robots building robots," he says. "And then we're really going to have nothing."

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