Updated for the 2026-2027 CFA® Level I curriculum.
A security market index tracks the performance of a defined group of securities. This reading asks you to explain why analysts and portfolio managers rely on indexes and to compare the broad categories of indexes available across markets. After reviewing this note, you should be able to match an index's stated purpose to its likely use and identify the broad asset-class types that indexes cover.
Quick Answer
Security market indexes serve five main uses: gauging market sentiment, acting as a proxy for measuring and modeling risk and return, supporting asset allocation decisions, benchmarking portfolio manager performance, and serving as the model for index-based investment products. Broad index types are organized by asset class, including equity, fixed income, commodity, and real estate indexes. An index's intended use shapes how it is built, which affects how you should interpret its returns.
Key Takeaways About Uses and Types of Security Market Indexes
Indexes exist to serve specific analytical or investment jobs, not just to report a price level.
The five common uses are gauging sentiment, proxying risk and return, informing asset allocation, benchmarking manager performance, and modeling index-based products.
Broad index types are grouped by asset class: equity, fixed income, commodity, and real estate.
An index's construction reflects its intended use. A sentiment gauge and a fund benchmark can look very different even if both cover the same market.
Comparing two indexes requires matching their purpose first, not just their asset-class label.
This note covers the broad overview. Weighting mechanics appear in Index Weighting Methods, while equity index families appear in Equity Indexes.
What You Need to Know for CFA Level I
Identify the five common uses of security market indexes when given a scenario.
Distinguish broad index types by asset class: equity, fixed income, commodity, real estate.
Explain how an index's stated purpose changes how you interpret its return.
Recognize when a question tests this broad overview rather than asset-class-specific index mechanics.
Avoid confusing "type" (asset class category) with "weighting method" (a separate concept covered elsewhere).
Common Uses of Market Indexes
Analysts, portfolio managers, and product providers use security market indexes for five main purposes.
Use | What It Means | Typical Application |
|---|---|---|
Gauge market sentiment | Index level or change signals investor mood | Media headlines, quick market checks |
Proxy for risk and return | Historical index data estimates return and volatility of an asset class | Capital market expectations, research models |
Asset allocation input | Index data feeds long-term allocation decisions | Setting target weights across asset classes |
Performance benchmark | Manager returns are compared to a matching index | Evaluating active manager skill |
Model for investment products | Index composition and weights are replicated in a fund | Index funds, ETFs |
Notice that the first two uses are about understanding markets, and the last two are about building or judging investment products. A single index can support more than one use, but the use in question determines what "matters" about the index at that moment.
Broad Types of Security Market Indexes
Index providers build indexes across several broad asset-class categories.
Index Type | What It Tracks | Common Challenge |
|---|---|---|
Equity indexes | A defined group of stocks, by market, sector, or style | Choosing constituents and float availability |
Fixed-income indexes | Bonds grouped by issuer type, maturity, or credit quality | Bonds trade less often, so pricing is harder |
Commodity indexes | Futures contracts on physical goods, not the goods directly | Returns depend on the futures curve, not just spot prices |
Real estate indexes | Property values or real estate securities | Properties are illiquid and hard to price frequently |
Each type solves a different measurement problem. Bonds and real estate are harder to price continuously than actively traded equities, so index providers use different data sources and update schedules depending on the asset class.
How Index Purpose Affects Interpretation
The same reported index return can mean different things depending on why the index exists.
An index built to gauge sentiment only needs to move directionally with the market. An index built to serve as a performance benchmark needs a defensible, rules-based method for selecting and weighting constituents, because a manager's compensation or reputation may depend on the comparison. An index built as the model for an ETF needs constituents that are actually investable in the stated weights, including enough trading volume to support fund flows.
Before interpreting a change in any index, ask what the index is for. A 2% rise in a broad sentiment gauge tells you general market direction. A 2% rise in the specific benchmark tied to a manager's mandate tells you whether that manager is ahead or behind, once you compare it to the manager's actual return.
How to Distinguish This Overview from Asset-Class-Specific Index Notes
This note covers the big picture: why indexes exist and the broad categories they fall into. It does not cover how a specific index assigns constituent weights or how equity indexes divide markets by geography, sector, or style. Price, equal, market-capitalization, and fundamental weighting belong to Index Weighting Methods. Equity index families belong to Equity Indexes.
If a question asks why an index exists or which broad asset class it tracks, you are in the scope of this note. If a question asks how an index calculates its value or how a change in one constituent's price affects the index level, you have moved into equity index construction, which is covered separately.
Worked Example
A wealth manager oversees a portfolio invested 70% in large-cap US stocks and 30% in investment-grade corporate bonds. Before a quarterly client review, the manager needs to do two things.
Task 1: Update the firm's long-term return and volatility assumptions used in next year's asset allocation review.
Task 2: Confirm whether the portfolio's active equity and bond managers added value over the past year.
Step 1
For the allocation review, the manager pulls long-run historical return and volatility data from a broad equity index and a broad investment-grade bond index. This matches the proxy-for-risk-and-return use, which then feeds directly into the asset allocation input use.
Step 2
For manager performance, the wealth manager compares the equity manager's one-year return to the same broad equity index and compares the bond manager's one-year return to the same broad bond index. This matches the performance benchmark use.
The manager relies on the same two indexes for two different jobs. One job estimates long-run assumptions. The other job judges short-run manager skill. The index type (equity or bond) does not change, but the use does, and that use determines what the manager should conclude from each comparison.
Common Exam Traps
Confusing index type with weighting method
Type refers to the asset class an index covers, such as equity or fixed income. Weighting method, such as price weighting or market-capitalization weighting, is a separate concept covered in Index Weighting Methods.
Reciting the five uses without matching them to the facts
Level I questions describe a scenario and ask which use applies. Listing all five uses from memory without connecting them to the stated facts will not answer the question.
Assuming one index serves every use equally well
An index built to gauge sentiment may use different constituents than one built to be an investable benchmark. The two roles are not interchangeable in practice.
Ignoring how index purpose changes interpretation
A rising index does not automatically mean a manager underperformed. The comparison only makes sense once you confirm the index matches the manager's actual mandate.
Practice Question
An analyst wants to select a broad market index that will primarily serve as the return and risk input used in the firm's asset allocation model. Which use of security market indexes best describes this application?
Benchmark for evaluating a portfolio manager's performance
Proxy for measuring and modeling the risk and return characteristics of an asset class
Model for constructing a new index-based investment product
Correct Answer: B
Using historical index data to estimate expected risk and return inputs for an asset allocation model is the proxy-for-risk-and-return use. This use directly supports building the assumptions behind allocation decisions.
Option A: Confuses the asset allocation input use with the performance evaluation use. Both rely on indexes, but performance evaluation compares actual manager results to a benchmark, not long-run assumptions.
Option C: Describes building an investable product, not developing risk and return assumptions for a model.
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FAQs About Uses and Types of Security Market Indexes
What is the difference between an index's use and its type?
Use describes the job the index performs, such as benchmarking a manager. Type describes the asset class the index tracks, such as equity or fixed income. A single index can have one type but support several uses.
Do all security market indexes work as investable benchmarks?
No. Some indexes are built mainly to gauge sentiment or to model asset-class returns and are not designed for exact replication. An index used as an investable benchmark or ETF model needs constituents that are actually tradable in the stated weights.
Where do index weighting methods fit in this reading?
Weighting methods such as price weighting and market-capitalization weighting are covered in Index Weighting Methods. Equity index families are covered separately in Equity Indexes. This note stays focused on broad uses and asset-class types.