There are many ways to classify stocks. Some investors think about growth stocks and value or dividend stocks. Or sort by market capitalization, mega cups, large caps, mid caps, and small caps. There are also more formal organizational technologies based on the stock market sector.
According to the most commonly used classification system, there are 11 stock market sectors. At the time of this writing, nine of these sectors were S&P 500 (^gspc 1.59%)) Year (YTD). Given that the S&P 500 is one of the most well-known stock market indexes, you may wonder how that is possible. The S&P 500 represents the most valuable US companies, but in some respects it does not represent the broader stock market well.
It is important to understand the structure of exchange-owned funds (ETFs) or index funds before you buy them.
Image source: Getty Images.
Sector differences
In recent years, the most valuable US companies have led the broader markets higher, and have more focused the S&P 500.
nvidia (NASDAQ: NVDA), apple (NASDAQ: AAPL)and Microsoft (NASDAQ: MSFT) It is made up of 19.6% of the S&P 500 on its own. Put it in Amazon (NASDAQ: AMZN), alphabet (NASDAQ: GOOG) (NASDAQ: Google), Meta Platform (NASDAQ: Meta), Broadcom (NASDAQ: AVGO), Tesla (NASDAQ: TSLA)and Netflix (NASDAQ: NFLX)that's 32.6% of the S&P 500.
All of these companies fall into the technology, consumer discretion, or communications sector, which accounts for 52% of the S&P 500. Technology alone accounts for 30.7%.
However, many of these stocks have slowed down the performance of the S&P 500 YTD. In fact, Apple, Amazon, Microsoft, Nvidia, and Tesla are negative YTDs and are dragging the S&P 500.
^spx Data based on data YCHARTS
Meanwhile, industry leaders in other sectors are on track. This will allow us to surpass the sectors that have so far surpassed the S&P 500 this year.
^ixv Data based on data YCHARTS
Reading tea leaves in sector
When previous market leaders begin to underperform their benchmark performance, it can be a sign that some people consider their stocks to be overvalued. So they can sell out from their names and rely on other pockets of the market for cheaper growth stocks, or switch to value and income stocks.
Based on whether it's advantageous or not, going in and out of sectors or themes is not a great idea for individual investors. Rather, a better approach is to recognize how a few companies move their S&P 500 and ensure that they see what constitutes an ETF or index fund before purchasing.
For example, the meta platform and alphabet account for an astonishing 48.5% Vanguard Communications ETF (nysemkt:vox) – A fund that reflects sector performance. Similarly, Amazon and Tesla account for over 40% Vanguard Consumer Diagentary ETF (nysemkt:vcr). Apple, Nvidia, Microsoft and Broadcom account for 48.3% Vanguard Information Technology ETF (nysemkt:vgt). When purchasing sector ETFs, it is worth understanding that only a handful of companies can drive profits and losses.
Many investors may purchase S&P 500 index funds due to their extensive exposure to the stock market. But even the S&P 500 is less diverse than before, given how big the large tech stocks are.
The top 10 companies by market capitalization of the S&P 500 account for 37.6% of the index. The top 25 companies also account for 50% of the index. That means only 5% of companies responsible for half of the S&P 500's move. So, if a low-weight company is on track, it could be hidden by the movements of large companies.
How concentration risk affects your portfolio
When purchasing individual stocks, it is essential to have a clear investment paper. This includes factors such as how the company works, how the market values it, how it accumulates in competition, and why it wants to be 3-5 years (or long) (or why it's a good fit for your portfolio based on risk tolerance and investment goals.
When purchasing an index fund or ETF, you certainly don't need to know the inside and outside of all holdings. After all, most investors buy these funds for extensive exposure to the general market, sector, or theme.
However, it is essential to know how the fund responds based on different market movements, and whether the portfolio will diversify or incorrectly lead to more focus.
For example, if 10% of your portfolio is investing in semiconductor stocks and you are satisfied with the size of your position, buying an S&P 500 index fund does not provide sufficient diversification as 7.8% of your index is invested in NVIDIA and Broadcom.
It is also worth noting that if you don't own top components in your index, your portfolio performance can vary significantly from the S&P 500. Therefore, comparing the way they stack with the index has little to do with stock picks.
The advantage of a few companies adds a focused risk element to the S&P 500. If you have a long-term time period, investing in the S&P 500 or individual Megacup technology stocks is still a solid idea. However, concentration risk can make the S&P 500 volatile if there are large sales in some of the main names. This is because we assume that it won't be volatile for risk aversion investors who choose S&P 500 index funds, especially because they own hundreds of shares.
Randi Zuckerberg, a former director of market development, Facebook spokeswoman and sister to Metaplatform CEO Mark Zuckerberg, is a member of Motley Fool's board of directors. John Mackey, former CEO of Amazon subsidiary Whole Foods Market, is a member of Motley Fool's board of directors. Suzanne Frey, an executive at Alphabet, is a member of the board of directors of Motley Fool. Daniel Fallver has no position in any of the stocks mentioned. Motley Fool has positions for Alphabet, Amazon, Apple, Meta Platforms, Microsoft, Netflix, Nvidia and Tesla, and is recommended. Motley Fool recommends Broadcom and the following options are recommended: A $395 call at Microsoft for January 2026 and a $405 call at short term Microsoft for January 2026. Motley Fools have a disclosure policy.
