Chapter 8: Indices and Benchmarking — Part 2: Index Construction and Stock Market Indices

8.4 Quantitative and Qualitative Index Methodologies

Index providers must establish objective, rules-based frameworks to govern the selection and weighting of index constituents. These frameworks consist of quantitative and qualitative criteria that ensure the resulting index is representative of its target market, highly liquid, investable, and replicable.

In the Indian equity market, the two most prominent index providers are Asia Index Private Limited (a joint venture between S&P Dow Jones Indices and BSE) and NSE Indices Limited (formerly known as India Index Services & Products Limited or IISL). The specific index construction methodologies for their flagship indices—the S&P BSE SENSEX and the NIFTY 50—illustrate how these criteria are applied in practice.

8.4.1 S&P BSE SENSEX Construction Methodology

The S&P BSE SENSEX is the oldest and most widely tracked equity index in India. It is designed to measure the performance of 30 of the largest, most liquid, and financially sound companies listed on the BSE (formerly Bombay Stock Exchange). The index is calculated using a free-float market capitalisation methodology.

1. The Eligible Universe

The initial pool of eligible stocks is derived directly from the constituents of the S&P BSE 100 Index.

• Treatment of Differential Voting Rights (DVRs): If an eligible company has issued Differential Voting Rights (DVR) shares, and these DVRs meet the index's eligibility criteria, they are aggregated with the company’s common stock for index construction purposes. The inclusion of DVRs can result in more than 30 individual share classes being traded within the index; however, the total number of unique parent companies in the S&P BSE SENSEX remains strictly fixed at 30.

2. Core Eligibility Factors

Stocks within the eligible universe must satisfy two strict liquidity and history thresholds to be considered for index inclusion:

• Listing History: The stock must have a listing history of at least six months on the BSE.
• Trading Frequency: The stock must have traded on every single trading day on the BSE during the six-month reference period.

3. Step-by-Step Index Construction Process

Once the eligible universe is defined and filtered, the index provider applies a five-step quantitative ranking and sorting process to select the final constituents:

• Step 1: Float-Adjusted Market Capitalisation Ranking All eligible companies are ranked based on their average six-month float-adjusted market capitalisation. The top 75 companies are identified.

• Step 2: Total Market Capitalisation Ranking All eligible companies are ranked again based on their average six-month total (full) market capitalisation. The top 75 companies are identified.

• Step 3: Annualized Traded Value Liquidity Filter The companies identified in Step 1 and Step 2 are combined into a single master pool. This consolidated list is sorted based on each stock's annualized traded value. Companies whose cumulative annualized traded value falls in the bottom 2% (representing a cumulative annualized traded value greater than 98% when sorted from highest to lowest liquidity) are excluded from selection.

  • Calculation Note: Annualized traded value is calculated by taking the median of the monthly medians of the daily traded values over the six-month reference period. This value is annualized assuming 250 trading days in a year.

• Step 4: Index Weight Filter The remaining companies are sorted by their average six-month float-adjusted market capitalisation. Any company whose estimated weight in the index would be less than 0.5% is excluded.

• Step 5: Selection Rules and Sectoral Representation The remaining pool is ranked by average six-month float-adjusted market capitalisation. The final 30 constituents are selected based on the following prioritisation rules:

  1. The top 21 companies (regardless of whether they are current index constituents or new entrants) are automatically selected with no consideration given to sectoral representation.
  2. Existing index constituents ranked between 22 and 39 are selected in order of the highest rank until the target count of 30 companies is reached.
  3. If the target of 30 companies is still not met, non-constituent companies ranked between 22 and 30 are selected, with preference given to companies whose sectors are underrepresented in the index compared to the sector representation of the S&P BSE All Cap Index.
  4. If the target of 30 is still not achieved, non-constituents are selected in order of their highest rank until the count reaches 30.

Note: All final additions and deletions are made at the sole discretion of the Index Committee, and constituents are weighted based on their float-adjusted market capitalisation.

8.4.2 NIFTY 50 Construction Methodology

The NIFTY 50 is the flagship index of the National Stock Exchange of India (NSE). It tracks the performance of a well-diversified portfolio of 50 blue-chip companies. Like the SENSEX, the NIFTY 50 uses a free-float market capitalisation weighting methodology.

To be eligible for inclusion in the NIFTY 50, a security must meet three rigorous quantitative criteria established by NSE Indices Limited:

1. Trading Frequency

The stock's trading frequency must be 100% over the preceding six months (i.e., it must have traded on every trading day).

2. Average Impact Cost Threshold

The security must have traded at an average impact cost of 0.50% or less during the last six months, for at least 90% of the observations, for a portfolio size of INR 10 crores.

• Understanding Impact Cost: Impact cost is a practical measure of market liquidity. It represents the actual transaction cost (or markup) an investor incurs when executing a transaction in a security in proportion to its index weight. Rather than being a fixed exchange fee, it is the percentage premium paid (when buying) or discount suffered (when selling) compared to the ideal market price.
• The ideal market price is calculated as: Ideal Price = (Best Buy Price + Best Sell Price) / 2
• The impact cost is the percentage deviation of the actual execution price from this ideal price. A low impact cost indicates high liquidity and deep order book volume.

3. Free-Float Market Capitalisation Rule

The company's average free-float market capitalisation must be at least 1.5 times the average free-float market capitalisation of the smallest constituent currently in the NIFTY 50 index. This ensures that new entrants are significantly larger than the bottom-ranked existing constituents, which reduces frequent index turnover.

Note: NIFTY 50 index values are calculated and disseminated in real-time, rounded to two decimal places.

8.5 Major Categories of Stock Market Indices

Equity markets feature a diverse array of indices designed to serve different investment mandates. These indices are classified based on their underlying coverage, style focus, currency denomination, and calculation methodology.

8.5.1 Broad-Based Indices

Broad-based (or broad market) indices represent an entire market or a highly significant portion of the investable equity universe. They typically cover multiple capitalization ranges (large, mid, and small-cap) to capture overall economic trends.

• NIFTY 500: Represents approximately 96.1% of the free-float market capitalisation of all stocks listed on the NSE (as of March 29, 2019).
• Russell 3000: A prominent US broad market index consisting of the largest 3,000 US-listed stocks, representing approximately 98% of the investable US equity market.

8.5.2 Market Capitalisation-Based Indices

These indices group stocks into specific size buckets based on their market capitalisation. As the valuation of companies fluctuates over time, stocks naturally migrate from one capitalization index to another during periodic reconstitutions. The key indices maintained on the NSE include:

• NIFTY 50 Index: A well-diversified index of 50 major companies reflecting overall market conditions. Prominent constituents include HDFC Bank Ltd., Reliance Industries Ltd., Tata Consultancy Services Ltd., and ITC Ltd.
• NIFTY Next 50 Index: Represents the 50 companies within the NIFTY 100 after excluding the NIFTY 50 constituents. Examples of constituents include Adani Green Energy Ltd., Avenue Supermarts Ltd., and Info Edge (India) Ltd.
• NIFTY 100 Index: Tracks the combined performance of the NIFTY 50 and the NIFTY Next 50.
• NIFTY 200 Index: Designed to reflect the combined behaviour of large-cap and mid-cap segments. It includes all constituents of the NIFTY 100 and the NIFTY Midcap 100.
• NIFTY 500 Index: Includes the top 500 companies selected based on full market capitalisation from the eligible NSE universe.
• NIFTY Midcap 150 Index: Represents the next 150 companies (ranked 101 to 250) based on full market capitalisation within the NIFTY 500, serving as the industry standard benchmark for mid-cap fund performance.

8.5.3 Style Indices: Value vs. Growth

One of the most significant developments in modern equity portfolio management is style-based investing. Portfolio managers categorize their investment philosophies as either Value or Growth, and index providers have developed style indices to benchmark these distinct strategies.

Ratios Used to Categorize Style:

Stocks are classified into value or growth style categories using key financial valuation ratios:

• Price-to-Earnings (P/E) Ratio: P/E Ratio = Current Price per Share / Earnings per Share
• Price-to-Book (P/B) Ratio: P/B Ratio = Current Price per Share / Book Value per Share
• Dividend Yield: Dividend Yield = Annual Dividend per Share / Current Price per Share

Comparison of Style Philosophies:

8.5.4 Capitalisation and Style Indices

To provide highly granular benchmarks, index providers blend capitalization ranges with investment styles. This yields six primary style-cap segments:

1. Large-Cap Value
2. Large-Cap Growth
3. Mid-Cap Value
4. Mid-Cap Growth
5. Small-Cap Value
6. Small-Cap Growth

These blended indices are essential for Category III AIF managers who pursue style-specific mandates (e.g., a small-cap growth strategy).

8.5.5 Sectoral Indices

Sectoral indices track the performance of specific industries or economic sectors, allowing investors to gauge relative sector strength and benchmark sector-specific portfolios. Prominent examples in the Indian market include:

• NSE Sectoral Indices: Nifty IT Index, Nifty Bank Index, Nifty FMCG Index, Nifty Pharma Index, Nifty Auto Index, Nifty Consumer Durables Index, and Nifty Financial Services Index.
• BSE Sectoral Indices: S&P BSE Energy, S&P BSE Auto, S&P BSE Realty, S&P BSE Finance, S&P BSE BANKEX, and S&P BSE Healthcare.

8.5.6 Total Return Index (TRI) vs. Price Return Index (PR)

A critical distinction in performance benchmarking is whether an index is calculated as a Price Return Index (PR) or a Total Return Index (TRI).

• Price Return Index (PR): Calculates index value based solely on the capital appreciation (share price movements) of its constituent stocks. It completely ignores any cash distributions, such as dividends.
• Total Return Index (TRI): Assumes that all cash dividends declared by constituent companies are immediately reinvested back into the index on the ex-dividend date.

Because equity investments generate returns through both capital gains and dividend income, investors must always benchmark their performance against the Total Return Index (TRI). Benchmarking an active portfolio against a Price Return Index artificially inflates the manager's outperformance (alpha), as the benchmark's returns are understated by the omitted dividend yield.

Mathematical Implementation of Total Return Index

To construct a TRI, dividend payouts are indexed on their ex-dividend date and reinvested proportionally across the index constituents.

1. Indexed Dividend Formula: Indexed Dividend = Dividend Payout / Base Capitalisation of Index
2. Total Return Index Calculation: Total Return Index = Previous TR Index * (1 + ((Today's PR Index + Indexed Dividend) / Previous PR Index) - 1)

Note: At inception, the base value of both the Price Return Index and the Total Return Index is identical. Over time, the TRI will systematically diverge upward from the PR index due to the compounding effect of reinvested dividends.

8.5.7 Dollar-Denominated Indices

Foreign institutional investors (FIIs) who invest in Indian equities face two distinct sources of return: local stock price movements and currency fluctuations (foreign exchange risk). To help these investors measure net returns in their own reporting currency, index providers construct currency-linked index variants.

• NIFTY50 USD: A US Dollar-denominated variant of the NIFTY 50 index. It is calculated in real-time by adjusting the NIFTY 50 index value for the daily USD/INR exchange rate.
• Formula: NIFTY50 USD Value = (Closing Value of NIFTY 50 * Exchange Rate on Base Date) / Exchange Rate for the Day
• Base Specifications: The base date of the NIFTY50 USD is November 3, 1995 (matching the NIFTY 50), with a base index value of 1,000 points.
• Other Variants: The NIFTY 50 is also computed in Australian Dollars (AUD) and Canadian Dollars (CAD).

8.5.8 Global Equity Indices: Market-Cap vs. GDP Weighting

For global investment mandates, index providers maintain broad indices covering multiple countries. These indices face a structural debate regarding country weighting methodologies.

Major Global Index Providers and Series:

• S&P Global Broad Market Index (BMI) Series: Launched in 1989, this series covers approximately 10,000 stocks across 25 developed and 25 emerging markets.
• MSCI World Index: Captures large and mid-cap representation across 23 Developed Markets (DM) countries. With 1,601 constituents, it covers approximately 85% of the free-float market capitalisation in each country.
• FTSE Global Equity Index Series: Covers over 16,000 large, mid, small, and micro-cap securities across 49 developed and emerging markets globally.

Rationale for GDP-Weighted Global Indices:

The vast majority of global indices are market-capitalisation-weighted. However, this approach has two key limitations:

1. Exclusion of Unlisted Economic Giants: Market-cap indices only account for listed equities. In many emerging markets, state-owned enterprises or massive private conglomerates remain unlisted despite contributing significantly to national GDP.
2. Developed Market Bias: Developed countries tend to have much higher market-capitalisation-to-GDP ratios than emerging and frontier markets. Consequently, market-cap-weighted global indices are heavily tilted toward developed nations, leaving emerging economies underrepresented relative to their actual economic output.

To address this, index providers offer GDP-Weighted Indices (such as the MSCI World GDP Weighted Index, launched on September 30, 1988). In these indices, country weights are derived from their annual Gross Domestic Product (GDP) rather than the aggregate market capitalisation of their stock exchanges, aligning the index with the real physical economy.

8.5.9 MSCI India Index

While domestic indices (like SENSEX and NIFTY 50) are ideal for local market participants, international fund managers managing multi-country portfolios require globally consistent country indices to ensure comparability. MSCI provides this standardized framework.

• MSCI India Index: Designed to measure the performance of the large and mid-cap segments of the Indian market.
• Constituents and Coverage: It features 86 constituents and covers approximately 85% of the total Indian equity universe's market capitalisation.
• Key Design Pillars: The construction methodology prioritises three key variables:
  1. Liquidity: Measured systematically using average impact cost.
  2. Investability: A function of constituent liquidity and the free-float weight of the securities, which determines the overall investment capacity of the index.
  3. Replicability: Ensures that institutional fund managers can passively replicate the index in physical portfolios without experiencing excessive tracking error.
• Review and Rebalancing Schedule: The index is reviewed quarterly in February, May, August, and November. During the semi-annual reviews in May and November, the large-cap and mid-cap capitalization cut-off points are recalculated, and the index is rebalanced.

Summary of Stock Market Index Categories

Important Terms & Definitions

1. Impact Cost: A measure of liquidity representing the percentage markup or transaction cost incurred when executing a trade of a specific size in a security compared to its ideal price.
2. Ideal Price: The simple average of the best buy price and the best sell price available in the limit order book: Ideal Price = (Best Buy + Best Sell) / 2.
3. Price Return Index (PR): An index calculation methodology that tracks only the change in stock prices, ignoring cash dividend distributions.
4. Total Return Index (TRI): An index calculation methodology that accounts for both share price movements and the immediate reinvestment of cash dividends on the ex-dividend date.
5. GDP-Weighted Index: A country-weighting scheme in global equity indices where country allocations are based on national GDP rather than equity market capitalisation.
6. Style Drift: A phenomenon where an active fund manager deviates from their declared investment style (e.g., a value manager buying expensive growth stocks). Style indices help detect this.

Candidates’ Exam-Relevant Takeaways

• 👉 S&P BSE SENSEX contains exactly 30 companies, but the inclusion of DVRs can result in more than 30 individual traded stocks in the index.
• 👉 SENSEX eligibility requires a minimum listing history of six months on the BSE and trading on every single trading day during the reference period.
• 👉 NIFTY 50 inclusion requires 100% trading frequency and an average impact cost of 0.50% or less over six months for 90% of observations on an INR 10 crore portfolio.
• 👉 NIFTY 50 new entrants must have a free-float market capitalisation of at least 1.5 times that of the smallest constituent in the index.
• 👉 Value stocks are defined by low P/E, low P/B, and high dividend yields; Growth stocks are defined by high P/E, high P/B, and low dividend yields.
• 👉 Style indices exhibit higher portfolio turnover than broad market indices due to the migration of stocks between categories as their valuation ratios change.
• 👉 Active equity funds must be benchmarked against Total Return Indices (TRI) rather than Price Return (PR) indices to ensure a fair, dividend-inclusive comparison.
• 👉 NIFTY50 USD uses the exchange rate on the base date of November 3, 1995, with a base index value of 1,000 points.
• 👉 GDP-weighted global indices help correct the structural bias toward developed markets found in standard market-capitalisation-weighted global indices.
• 👉 The MSCI India Index has 86 constituents covering approximately 85% of the Indian equity market capitalisation, and is reviewed quarterly (February, May, August, November).