A recent change in the Nifty 50 Value 20 index’s methodology has prompted questions about the stability and reliability of factor funds, highlighting the need for investors to reconsider how they monitor and interpret these indices.
A quiet but important change in the Nifty 50 Value 20 index has revived an awkward question for investors in factor funds: what happens when the rulebook changes after you have already bought in?
The index was built to capture value stocks from the Nifty 50 universe, but its definition of value has not stood still. A methodology document available from NSE India shows that the older version used return on capital employed, price-to-earnings, price-to-book and dividend yield, with return on capital employed carrying the biggest weight. The newer version has moved to a different set of measures: earnings-to-price, book-to-price, sales-to-price and dividend yield, each weighted equally. It also shifts from annual review to semi-annual rebalancing in June and December.
That matters because a factor index is not just a list of stocks; it is a rule set. In this case, the rule set appears to have moved closer to a conventional value screen and away from a blend that also rewarded quality. The earlier design had a strong quality tilt through return on capital employed, a measure that can favour asset-light businesses such as information technology and consumer companies. That kind of screen can also be awkward for banks, where the balance sheet structure makes the ratio less intuitive. Under the revised model, the signal is more narrowly tied to valuation.
The practical impact has already shown up in portfolio composition. Monthly disclosures from Nippon AMC suggest the index’s sector mix changed sharply between May and June 2026, with banking weight rising while software exposure fell steeply. That kind of shift underlines the broader risk in factor investing: even if a fund tracks the benchmark exactly, the benchmark itself may no longer resemble the one investors thought they had bought. The author of the lead article argues that the June 2026 rebalance was likely the first to use the new methodology, although the NSE documents available publicly do not spell out when or why the change was made.
Academic and industry research has long warned that this is not a trivial issue. A study highlighted by Scientific Beta and Scientific Analytics found that methodological changes in factor indices are common enough to alter performance in meaningful ways. S&P Dow Jones Indices has also noted that factor exposure depends not just on the factor definition itself but on how often an index is refreshed. By contrast, a plain market-cap index such as the Nifty 50 is far less exposed to this problem because its core definition is simple and stable: the largest companies remain the largest companies unless their market value changes.
For investors, the lesson is not necessarily to avoid factor funds entirely, but to recognise that they rely on a maintained recipe rather than a fixed law. If the recipe changes, the historical case for owning the fund may need to be reconsidered. That is especially true for investors who expected a specific style exposure, such as quality-value, but may now be getting something else. As the lead article argues, factor products may belong in a satellite allocation, not the centre of a portfolio, and they warrant periodic checks to see whether the methodology still matches the original thesis.
Disclaimer: This article is intended to inform and educate, not to recommend or endorse any financial product, investment or strategy. Please consider your own financial circumstances and seek professional advice where appropriate before making financial decisions.
