What is a stock index? – Forbes Advisor

A stock index tracks the ups and downs of a chosen group of stocks or other assets. Viewing the performance of a market index provides a quick way to see the health of the stock market, guides financial companies through creating index funds and exchange-traded funds (ETFs), and helps you measure the performance of your investments.

What is a market index?

A market index tracks the performance of a particular group of stocks, bonds or other investments. These investments are often grouped around a particular sector, such as technology stocks, or even the stock market in general, as is the case with the S&P 500, Dow Jones Industrial Average (DJIA), or Nasdaq.

There is no set size when it comes to market indices. The DJIA only lists 30 stocks, while the CRSP index has more than 3,700. What is important is that each contains a sample size large enough to reflect the general behavior of the economic swath they intend to represent.

How stock indices are composed

Each stock index uses its own formula to determine which companies or other investments to include.

Indices that measure the performance of broad swaths of the market can only include companies that rank highly in terms of market capitalization or the total value of all their outstanding shares. Alternatively, they can be selected by a committee of experts or simply represent all stocks traded on a particular exchange.

Once an index manager has determined which companies to include, he must determine how those companies will be represented in the index, a factor known as index weighting. Depending on the weighting, all companies included in an index may have an equal impact on index performance or a different impact based on market capitalization or share value.

The three most common index weighting models are:

• Weighted Market Cap: In a market capitalization weighted index, the index more strongly represents stocks with higher market capitalizations. With this structure, large companies have a greater influence on the performance of the index.
• Weighted equally: In an equally weighted index, the index treats all components the same. This means that the performance of every company affects the index to the same extent, whether they are incredibly large or incredibly small companies.
• Price weighted: A price-weighted index assigns a different weight to each company based on its current share price. Companies with higher stock prices have more leverage in these indices, regardless of how big or small the companies actually are.

Main stock indices

There are thousands of indices in the investment universe. To help you find your way, here are the most common indexes you are likely to encounter:

The S&P 500 Index

One of the most well-known indices, the S&P 500, tracks the performance of 500 top US companies, as determined by a commission at S&P Dow Jones Indices. The S&P 500 is a market capitalization weighted index.

The Dow Jones Industrial Average

The DJIA is relatively narrow, tracking the performance of just 30 US companies as selected by S&P Dow Jones Indices. Stocks within the DJIA come from a variety of sectors, from healthcare to technology, but are united in that they are all blue chip stocks. This means they have a history of strong financial performance. The DJIA is one of the few price-weighted market indices.

The Nasdaq 100

The Nasdaq 100 tracks the performance of 100 of the largest and most actively traded stocks listed on the Nasdaq exchange. Companies within the Nasdaq can operate in many different sectors, but they generally tend towards technology and do not include members of the financial sector. The Nasdaq 100 uses a market cap weighting.

The NYSE . Composite Index

The NYSE Composite Index is a comprehensive index that tracks the performance of all stocks traded on the New York Stock Exchange (NYSE). The index is adjusted for the market capitalization weighting.

The Russell 2000 Index

While other stock indices focus on the largest companies in a particular segment, the Russell 2000 measures the performance of 2,000 of the smallest publicly traded domestic companies. The Russell 2000 is a market capitalization weighted index.

The Wilshire 5000 Total Market Index

The Wilshire 5000 Total Market tracks the performance of the entire US stock market. The index is weighted by market capitalization.

Different types of market indices

While the indices discussed above are generally used as proxies for the general stock market, there are countless other indices, many of which are tailored to very specific market segments.

• Environment, social and governance: ESG (Environmental, Social and Governance) indices target companies that score well in the way they treat the environment, their employees, their management and society as a whole.
• Global indexes: As their name implies, global indices allow you to track the collective performance of all companies in the world.
• National indices: Just as the major stock indices above track the performance of the US market, there are indices that track the highs and lows of companies in almost every country.
• Growth indices: Growth indices track the performance of leading growth stocks, or those of companies that are seeking to grow faster than the overall market.
• Value indices: Value indices, on the other hand, group companies that are believed to be undervalued by investors based on their finances.
• Sector indices: Sector indices are designed to track the performance of specific sectors, such as technology, finance, healthcare, consumer goods and transportation.

How to invest in stock indices

Because they track the performance of a mix of companies and investments, funds based on leading indices are considered an excellent way to invest quickly, easily and cheaply. Index funds and exchange-traded funds (ETFs) provide access to a ready-made diversified portfolio of stocks and bonds and are what many investment gurus, such as Warren Buffett, swear by.

The great thing about index funds and ETFs is that you can invest in them with any amount of money at just about any brokerage. Not sure where to start? Check out our list of the best brokers.

If you’re not sure which investment options are best for you, talk to a financial planner who can help you create a personalized plan based on your goals. Or check out our ranking of the best index funds.