Types of Stock Market Indices

A stock market index is a statistical measure that reflects the price performance of a selected group of securities. In India, indices are compiled by recognised entities such as NSE, BSE and SEBI‑approved index providers. The index value is derived from the market prices of its constituent stocks and is expressed as a single number, making it easier to track market trends.

Indices serve three core purposes: (i) they act as a benchmark for portfolio performance, (ii) they provide the underlying for index‑based derivatives, and (iii) they help investors gauge the health of specific market segments. For the NISM exam, recognising the purpose of an index is essential because many questions link index behavior to futures pricing and risk management.

Exam‑wise, you may be asked to identify which index best represents a particular market segment or to calculate the impact of a price change on the index value. Remember that an index does not represent a tradable security itself; rather, it is a reference point.

Indices can be grouped based on the breadth of the market they cover. A broad‑based index includes a large number of stocks across various sectors, providing a holistic view of the market. Examples include the NIFTY 50 (large‑cap) and the BSE Sensex (top 30). These are frequently used as benchmarks for equity portfolios.

Beyond broad‑based indices, the market is segmented into large‑cap, mid‑cap and small‑cap indices. Large‑cap indices track the performance of the biggest companies by market capitalisation, while mid‑cap and small‑cap indices focus on mid‑sized and smaller companies respectively. The NIFTY Midcap 100 and NIFTY Smallcap 250 are typical illustrations.

Understanding the coverage helps you answer questions that ask which index best reflects the performance of a particular investment style. A common mistake is to assume that a sectoral index also captures the entire market, which it does not.

Weighting determines how much each constituent influences the index value. The three most common methods are price‑weighted, market‑capitalisation weighted and equal‑weighted. In a price‑weighted index, stocks with higher share prices have a larger impact, exemplified by the Dow Jones Industrial Average (though not used in India).

A market‑cap weighted index assigns weights proportional to each company’s total market capitalisation. This is the methodology behind the NIFTY 50 and BSE Sensex. The larger the company, the greater its contribution to index movements.

Equal‑weighted indices give every constituent the same weight regardless of size. This approach reduces concentration risk and is useful for assessing the average performance of a group of stocks. The NIFTY 100 Equal Weight Index is an example.

Sectoral indices track a specific industry or sector. For instance, the NIFTY Bank index reflects the performance of major banking stocks, while the NIFTY IT index captures information technology firms. These indices help investors gauge sector‑specific trends and are often used as underlying for sector futures.

Thematic indices go a step further by grouping stocks based on a common investment theme rather than a traditional sector. Examples include the NIFTY ESG (Environmental, Social, Governance) index and the NIFTY Low‑Volatility 30 index. Themes can be based on sustainability, dividend yield, or volatility characteristics.

In the exam, you may need to match an index to its underlying theme or sector. A typical mistake is to confuse a sectoral index with a thematic one; remember that thematic indices are driven by investment ideas, not pure industry classification.

All equity derivatives on Indian exchanges are based on an underlying index. Index futures and options derive their value from the index level, not from the individual stocks. This makes them efficient tools for hedging or speculating on the overall market direction.

The pricing of index futures follows the cost‑of‑carry model: Futures Price = Index × e^{(r - d)T}, where r is the risk‑free rate, d is the dividend yield, and T is time to expiry. While the exact formula is not required here, knowing that the index level is the starting point for all calculations is vital.

Exam questions frequently present a scenario where a client wants to hedge a portfolio using NIFTY futures. You must identify the correct underlying (NIFTY 50) and understand that the contract size (e.g., 75 × index value) translates the index movement into rupee terms.

Use the acronym W‑S‑T to recall the three primary classification dimensions: Weighting method, Sector/theme, and Type of coverage (broad, large‑cap, mid‑cap, small‑cap). When you see a question, mentally map the index to these three buckets.

Another handy tip is the “5‑15‑30” rule for Indian indices: roughly 5 major broad‑based indices, 15 sectoral indices, and 30 thematic indices are actively traded on NSE. This helps you eliminate options quickly.

Finally, remember that the divisor in the index formula is adjusted for corporate actions (splits, bonuses). The divisor ensures continuity of the index value, a point often asked in regulatory‑focused questions.