When you step back and look at the stock market over the last 100 years, what you will find is that a tiny group of publicly traded companies has accounted for nearly all of the profits for investors over the entire century.

Most of the top performers are tech companies, headed by Apple, Nvidia and Microsoft. What’s startling is that both Tesla and, if only briefly, SpaceX, two of Elon Musk’s companies, have muscled their way onto that list of superb performers.

While these elite stocks churned out spectacular returns, more than 96 percent of the stock market did virtually nothing for investors over long periods. This vast majority of stocks couldn’t even match the 3.3 percent average return of one-month Treasury bills — basically, the return you could get month-by-month over those 100 years, without taking any appreciable risk.

These findings come from the latest update to a long-running study by Hendrik Bessembinder, a finance professor at Arizona State University who has provided a trove of essential and provocative data about stock market investing. The study has aimed to ferret out long-term wealth creators since 1926, when the data available to Professor Bessembinder begins. The rise of the tech giants, and the relative decline of every other sector of the market, has radically changed the rankings over the last decade, and over shorter periods as well.

For example, Tesla didn’t make the list of top wealth creators nine years ago, when an earlier version of the study ended. The firm now ranks ninth among all publicly traded companies over the century. Even more striking, when Professor Bessembinder ran the numbers at my request on June 16, a few days after SpaceX’s initial public offering, the company made the top 30 all-time list, though its falling share price has since moved it out of that rarefied world.

“We’ve had very high returns for extraordinarily large firms in recent years, and the first few days of SpaceX as a public company were a case study of that,” he said. “To me, the most striking thing over the last nine years is that not only is wealth creation highly concentrated in just a few companies, but that the trend has been accelerating.”

The Implications

Back in 2017, I wrote about the first version of Professor Bessembinder’s work on investing. It showed then that the obstacles facing individual stock pickers were formidable. Most companies’ shares failed to outperform basic Treasury bills. A small proportion of great performers buoyed the entire market, but knowing in advance which stocks would be the winners was a difficult feat.

So I concluded that for a great majority of investors, it was much less risky to avoid stock picking entirely and instead invest with diversified low-cost mutual funds, particularly index funds mirroring the entire market.

But Professor Bessembinder’s findings also made it clear that there were vast riches to be made for those skilled or lucky enough to make the right choices: If you picked the very best performers, and avoided most losers, you would do extraordinarily well.

Those two insights remain true today, and perhaps even more so. I still think most people will be better off buying a small part of the entire stock market, a practice that I continue to follow myself. But the potential for gaining enormous wealth tempts millions of investors who scoop up shares of hot individual stocks like SpaceX. You will have to decide what’s best for you.

Defining Terms

In the first study, Exxon Mobil was the top performer from 1926 through 2016, followed by Apple, Microsoft, General Electric, IBM, Altria Group, Johnson & Johnson, General Motors and Walmart. That list depicted a diverse mosaic of the economy, with old companies dominating, aside from two upstarts, Apple and Microsoft, which had I.P.O.s in the 1980s.

Now Professor Bessembinder has 100 years of data, with returns from 1926 through December.

Just to put the SpaceX I.P.O. in perspective, he has updated the returns, applying the same methods he has used for all publicly traded stocks tracked over the last century. His approach accounts for stock dividends and buyouts, and the comparison with Treasury bills includes an inflation adjustment.

“Lifetime wealth creation,” as Professor Bessembinder defines it, is connected not just to share performance but also to a company’s total market valuation. This means that an increase of 10 percent in the share price for a giant has a far greater effect on total wealth creation than a 10 percent increase by a company with a small value in the market.

That’s important because tech companies have become giants, including SpaceX, which has been publicly traded only since June 12 but has a market capitalization of more than $2 trillion. When tech shares make big moves, 100 years of market returns need realignment.

An Entire Century

The economy has changed in the nine years since the first study. More than ever before, the pack of leaders is dominated by tech stocks, with only two traditional companies, Exxon Mobil and Walmart, remaining in the top 10 for the entire century.

Here are the leaders from 1926 through December, including their lifetime wealth creation and the percentage of the $91 trillion in total stock market wealth for which each was responsible:

Picking these stocks, and only these stocks, at their inception and riding them forever would have been a brilliant strategy. But in addition to needing remarkable perspicacity in the first place, sticking with the winners also required nerve, because even the greatest stocks periodically plunged steeply in value.

While a vast majority of companies didn’t perform well enough to justify this agita, a relative handful made up for all the rest, starting with Apple. It was founded in 1976, went public in 1980, and, on its own, accounted for 5.5 percent of the total net wealth generated for investors in the entire stock market since 1926.

Perhaps more astonishing was the performance of Nvidia, which makes advanced chips for artificial intelligence. The firm didn’t even exist as a publicly traded company until January 1999. Yet it has performed so well since that it ranks close behind Apple in the 100-year ranking, accounting for 5 percent of net investor profits in the last century.

Concentration

The stock market has changed in the last nine years, in ways that, I think, make the broad implications of the original study much stronger.

Consider that in the new, 100-year version of the study, just the top two companies, Apple and Nvidia, accounted for 10 percent of the wealth creation through December. In the years from 1926 through 2016, it took five companies to reach 10 percent of total shareholder wealth.

The significant differences of the last nine years are manifest in other ways. Add up the net wealth creation of the top 10 stocks in the new list: It comes to 29 percent of the total for the entire century. In the earlier study, the top 10 stocks amounted to only 17.1 percent of total wealth.

What accounts for all these changes is the explosive growth of tech stocks.

I’ve pointed out the dangers of this concentration of wealth in the markets before. Diversifying investments is more important than ever, yet it’s difficult to achieve true diversification, now that artificial intelligence and semiconductors have dominated a variety of markets globally.

The rise of SpaceX accentuates the issue. The company is so big and so richly valued, that making a large individual bet on it is risky. History now tells us that the bounteous wealth generated by such tech stocks poses a hazard on a truly grand scale.