The lonely green bar on this chart says it all

It's been a rough few months as stocks saw a bout of dramatic and capricious swings throughout August and September following warnings of global economic deceleration.

By the end of all of that, the broad market was down 6.7% year-to-date by the end of September.

However, that headline number alone doesn't reveal too much about what's actually happening in the economy.

In his latest slide deck to clients, Oppenheimer Asset Management Research's chief market strategist John Stoltzfus shared as chart showing the S&P 500 returns broken up by different sectors.

Basically every single sector was down year-to-date by the end of September - except for one.

"Over the first nine months of the year, Consumer Discretionary was the only sector showing positive price returns," Stoltzfus pointed out (which you can see in the chart above.)

This shouldn't come as a surprise to those who keep their eyes glued to the US economic data, as the US consumer has frequently been cited as a source of strength in the last few months. Indeed, the bulk of the recent months' personal spending data has been robust, even amid what appears to be a recession in manufacturing.

This even jibes with China's economy, whose slowdown has been characterized by its shift from investment to consumption. This international observation makes sense for the S&P 500 because half of S&P 500 revenues are generated abroad.

Returning to the US consumery, RBC Capital Markets chief US economist Tom Porcelli analyzed how the US economy would be affected by an ailing international economy, and he observed that the strength of the American consumer alone was more than offsetting the entirety of the economic fallout from the global slowdown.

And he isn't the only one to point to the strength of the US consumer. Some of Wall Street's biggest bulls, including David Rosenberg, chief economist and strategist at Gluskin Sheff, and FundStrat's Tom Lee have suggested that the US consumer's robustness and size is enough to offset the effects of a slowing China.

But, that was then

The fact that American consumers have been an economic powerhouse over the last nine months does not automatically mean that they will continue to be so.

According to the New York Fed's latest monthly Survey of Consumer Expectations, American consumers are feeling increasingly pessimistic about their future spending.

As of September, the median household sees its spending growing just 3.18%, the lowest level in the survey's two year history.

Even Walmart's CEO Doug McMillion didn't seem to enthused when asked to address the US economy.

In any case, the US consumer has been going strong for the first nine-months of the year - strong enough to offset any negative effects of the turbulent international economy. Again, there's no guarantee that this will continue.