Well, the DJIA has tracked the S&P 500 remarkably well through time. As the longest-running important stock market index, the DJIA allows for historical comparisons that stretch back over 100 years. That’s useful. There is a nostalgic comfort in thinking that the same single number, composed of a potpourri of well-known companies nominally headquartered in this country, represent the American role in the massively complex, globalized economy.

However: The index probably can’t include the really high-priced stocks like Google and Amazon. Back in 2012, Adam Davidson argued that the index isn’t even a good measure of the companies that it contains, because the price of an individual share of a company is not the best measure of its value to investors. If all you do is add up the share prices and then divide, you get strange results. Given the same market value, a company with fewer shares outstanding will have a higher share price—and therefore a bigger impact on the index—than a company with more shares outstanding. And if you have a huge market cap and fewer shares outstanding, then you get share prices like Amazon’s, which is trading over $1,750 today. Walgreens shares are trading below $70. Would it make sense to have Amazon’s impact on the index hit at more than 25 times Walgreens’s? What’s the point of a bundle of stocks at that point?

Nonetheless, this is the way that the DJIA has done things before, so that’s the way it continues.

Besides, share prices are, themselves, becoming detached from the traditional measures of value for companies. Digital companies, in particular, are valued differently from industrial giants like GE, three business-school professors argued in the Harvard Business Review.

“Accounting earnings are practically irrelevant for digital companies,” the professors wrote. The things that investors value about Amazon and Facebook—the chance they will get huge and dominate markets with incredibly high margins—are not reflected in earnings reports.

“In another study, we show that earnings explains only 2.4 percent of variation in stock returns for a 21st-century company—which means that almost 98 percent of the variation in companies’ annual stock returns are not explained by their annual earnings,” they continue.

For example, for fiscal year 2017, Costco had earnings per share of $6.08. Amazon had earnings per share of $6.15. Costco’s market value is $91 billion; Amazon’s is $844 billion.

Amazon certainly seems like a more important company. But is it 9.3 times more important? The mathematical precision of the stock market, no matter how it’s indexed, just does not map well onto the messy realities of the economy.

If what we want is a snapshot of the economy, like the real one that you and I live and work in, then the Dow Jones Industrial Average, and the rest of the stock market, are probably not the best indicators for the average American.