Factor investing and smart beta: beyond market-cap weighting

A traditional index weights companies by market capitalisation: the bigger the company, the more you own. That is a choice, not a law of nature — and it has an awkward property. You automatically own more of whatever has already gone up.

Factor investing asks the obvious follow-up: if you are going to weight by something, why that?

What a factor is

A factor is a characteristic that academic and practitioner research has associated with returns across long periods and multiple markets. The ones that recur:

• Value — cheap on earnings, book value or cash flow.
• Momentum — recent relative strength continues, over intermediate horizons.
• Quality — high profitability, low leverage, stable earnings.
• Low volatility — calmer stocks have historically delivered better risk-adjusted returns than their volatility would suggest.
• Size — smaller companies, over very long periods.

A smart beta or factor index fund builds a rules-based index that tilts toward one or more of these, then tracks it passively. You get a systematic tilt without paying discretionary active fees.

The honest framing

This is the part usually skipped.

Factor investing is active management with the discretion removed. You are deviating from the market portfolio in a deliberate, disclosed, rules-based way. That is genuinely different from a manager’s judgement — it is transparent, repeatable and cheap — but it is not passive in the sense a broad index fund is passive.

Which means it carries an active manager’s central problem: the tilt can underperform, and it can do so for a very long time. Value spent the better part of a decade lagging globally. Momentum crashes hard at turning points. Low volatility lags badly in strong bull markets.

If a factor never underperformed, it would be arbitraged away. The underperformance is the mechanism. Which means the only way to earn it is to hold through the stretch where it makes you look foolish — and most investors do not.

Where it fits

Factor funds are satellites, not cores — see core and satellite.

• Size it as a tilt, not a replacement. A broad market core with a modest factor sleeve is a coherent structure; an all-factor portfolio is a set of concentrated bets.
• Hold one horizon, not one cycle. These need long periods to work, and switching factors after a bad stretch is the same chase that damages active-fund investors.
• Prefer a factor you can explain. If you cannot say why the premium should persist, you will not hold it through the drawdown.

Multi-factor funds combine several tilts, which smooths the ride because factors underperform at different times — at the cost of diluting any single one and making attribution harder.

What to check before buying one

The index construction is the product, so read it:

• How is the factor defined? Two “value” indices can use different metrics and produce meaningfully different portfolios.
• How often does it rebalance? More frequent capture of the factor means higher turnover and cost, particularly for momentum.
• How concentrated is the result? Some factor indices end up heavily weighted to one or two sectors, which is a sector bet wearing a factor label.
• What is the expense ratio and the tracking difference? A factor premium is worth a couple of percentage points at best in expectation. A fee and a tracking lag can consume most of it.
• How long has the Indian version existed? Many are recent, and backtested index history is not the same as live performance with real flows and costs.

Pitfalls to avoid

• Believing backtests. Every published factor index looks excellent in simulation; that is the selection criterion for publishing it.
• Buying a factor after its good run. The most reliable way to earn the underperformance without the premium.
• Treating it as passive because it is rules-based. It is a systematic active bet.
• Stacking factor funds until you have re-created the index. Own three or four tilts and you own the market, at a higher fee.
• Confusing a thematic fund with a factor fund. A “manufacturing” index is a sector bet, not a factor.

Key takeaway

Factor investing is a legitimate middle ground — a disclosed, rules-based tilt away from market-cap weighting, at a fraction of discretionary active cost. It is also active risk by another name, and every factor has long stretches of underperformance that are the reason the premium is supposed to exist. Use it as a sized satellite around a broad core, choose a factor whose logic you can state, and commit to holding it through the years when it looks wrong — because that is the only period in which it is actually being earned.