Passive Investing Is a Label, Not a Literal Description

There Is No Such Thing as Passive Investing

"I'm a passive investor." It is one of the most common self-descriptions in personal finance. It means: I buy index funds, I do not pick stocks, I keep costs low, and I stay the course. That is a good investment philosophy. But the word "passive" is doing something misleading. It implies that no decisions are being made. In reality, someone made every decision. They just made them upstream, before you bought the fund.

Who chose the index? Who set the inclusion rules? Who decided on the weighting scheme, the reconstitution schedule, the profitability screen, and the committee governance? Who decides when to add Tesla or remove a company that no longer qualifies? Those are not passive questions. They are active design choices embedded in the product you are holding.

Adriana Robertson's research puts it precisely: far from being passive, index investing is often a form of delegated management. The investment choices do not disappear. They are pushed upstream into index design, governance, and implementation.

Legal Passive vs. Economic Passive

In regulatory and product-label terms, "passive" means the fund adviser follows a stated index rather than exercising broad stock-picking discretion. The SEC describes traditional index funds as "passive" but also notes they can use full replication or sampling, may use derivatives, and that non-traditional index funds track custom-built indices using criteria that active managers might also use.

In economic reality, someone still made active choices about:

• What counts as the investable universe
• How securities are weighted (cap-weight, equal-weight, factor-weight)
• When entries and exits happen (quarterly, as-needed, annually)
• What profitability or style screens apply
• How corporate actions are handled
• When methodology changes occur

The distinction matters because two funds can both be marketed as "passive U.S. equity" and still deliver meaningfully different portfolios because their index architects made different decisions.

The Evidence: Every Index Has Discretion

Robertson's research found that, on average, there were about five funds per benchmark index in the U.S. market, and 79.4% of indices were used by only a single fund. Every one of the 600+ indices in her comprehensive sample gave the index provider at least some discretion. Investors think they are buying "the market." They are buying a portfolio shaped by a specific rulebook written by specific humans at a specific index provider.

In a follow-up study, Robertson and Molk found that S&P 500 index funds' actual holdings differed from the index by 1.7% to 7.5% in Q4 2022, amounting to almost $61.5 billion in discretionary investment decisions across those funds. Even the most "passive" fund in America exercises meaningful discretion that most investors do not recognize.

Three "Passive" Indices, Three Different Designs

The differences between popular indices illustrate the point. All three of these are used by funds marketed as "passive U.S. equity":

The S&P 500 requires positive GAAP earnings and gives a committee the power to override rules as needed. CRSP uses objective, transparent rules with quarterly rebalancing and "packeting" to reduce turnover. Russell reconstitutes annually. All three are "passive." All three make different choices about what counts as the market, when to add or remove stocks, and how much human judgment to involve.

The Discretion Spectrum

Rather than a binary "passive vs. active" distinction, the reality is a spectrum of where the discretion lives:

The key distinction is not "passive vs. active" but "where does the discretion live and how transparent is it?" Broad market indexing has the least adviser discretion. Discretionary stock picking has the most. Systematic active (Avantis, Dimensional) sits in between: the adviser makes choices, but they are embedded in a transparent, repeatable, rules-informed process rather than case-by-case human judgment.

Avantis explicitly describes AVUV as an actively managed ETF that does not seek to replicate a specified index, using current market prices and company financials to identify differences in expected returns. Dimensional similarly describes its ETFs as active transparent ETFs that pair the benefits of indexing with the flexibility of systematic investing. That is very different from a discretionary stock picker who relies on analyst narratives and macro calls.

Who Is Actually Making the Decisions?

For a "passive" S&P 500 index fund, the decision chain is:

1. S&P Index Committee decides which companies qualify (profitability screen, market cap, domicile, float, sector balance) and when to add or remove them.
2. S&P methodology team reviews and updates the rulebook annually. Changes affect every fund tracking the index.
3. Fund sponsor (Vanguard, BlackRock, etc.) decides on implementation: full replication vs. sampling, securities lending, derivative use, trading timing.
4. Investor decides to buy and hold. This is the only step typically labeled "passive."

Three of the four steps involve active human judgment. The investor's decision to buy and hold is passive. Everything upstream is not.

Why This Does NOT Mean Indexing Is Bad

This is the most important section. The argument is not "therefore avoid index funds." Robertson herself notes that index funds tend to have lower management fees and may be better for many investors than high-fee discretionary active funds. SPIVA reports that in 2025, 79% of active large-cap U.S. equity funds underperformed the S&P 500.

Broad, low-cost, market-cap-weighted indexing remains the most nearly passive option available. It minimizes adviser discretion, trading costs, tax drag, and behavioral mistakes. It is just not literally passive in the way the marketing implies. The hidden choices are there. They just happen to be reasonably good choices for most investors most of the time.

The practical takeaway is to understand what you own, not to abandon indexing. If you hold VOO, know that an S&P committee with a profitability screen and discretionary add/remove authority is making decisions on your behalf. If you hold VTI, know that CRSP uses objective rules with quarterly reconstitution and packeting. Neither is wrong. Both are active choices made on your behalf.

You can examine your portfolio's actual factor exposures and understand what is driving your returns in Summitward's portfolio analysis. The Carhart 4-factor regression shows your market, size, value, and momentum loadings, revealing the implicit bets embedded in your "passive" holdings.

Frequently Asked Questions

Is index investing the same as passive investing?

In industry terminology, yes. In economic reality, no. Index investing follows a rulebook, but someone designed that rulebook. The inclusion criteria, weighting scheme, reconstitution schedule, and committee governance are all active design choices. Robertson's research calls it "delegated management," which is more accurate.

Does the S&P 500 have a profitability screen?

Yes. Companies must have positive GAAP net income from continuing operations for the most recent quarter and for the sum of the most recent four consecutive quarters. This means unprofitable companies are excluded, which is an active screening decision that many investors do not realize exists.

Do different S&P 500 funds hold the exact same stocks?

Not always. Molk and Robertson (2024) found that S&P 500 index fund holdings differed from the index by 1.7% to 7.5% in Q4 2022. Even funds tracking the same index exercise meaningful implementation discretion.

What is the difference between systematic active and discretionary active?

Systematic active (Avantis, Dimensional) uses transparent, repeatable rules to select and weight stocks based on factors like size, value, and profitability. Discretionary active relies on individual portfolio managers making case-by-case judgments. Both are "active," but systematic active is closer to indexing in its process transparency.

Should I stop using index funds?

No. Broad, low-cost, market-cap-weighted index funds remain an excellent default for most investors. The point is not that indexing is bad. The point is that "passive" is an incomplete description, and understanding the choices embedded in your index helps you make better decisions about what you own.

Key Takeaways

• "Passive investing" is a legal/marketing label, not an economic description. Someone chose the index, the rules, the screens, and the reconstitution schedule. Those are active design choices.
• 79.4% of indices are used by a single fund. Every one of 600+ indices studied gave the provider discretion. You are not buying "the market"; you are buying a specific rulebook.
• Even S&P 500 funds deviate from the index. Holdings differed by 1.7-7.5% in Q4 2022. Implementation itself involves discretion.
• The real question is "where does the discretion live?" Not "is this active or passive?" Broad indexing has the least adviser discretion. Systematic active has transparent process discretion. Discretionary active has the most person-dependent discretion.
• This does NOT mean indexing is bad. 79% of active large-cap funds underperformed the S&P 500 in 2025. Broad, low-cost indexing remains excellent. The label is just misleading.

Related Guides

• The S&P 500 Is Passive for You, But Not Under the Hood applies the delegated-management idea to the S&P 500 specifically, and the VOO/VTI/VT product choice.
• How Financial Sales Pitches Hide the Real Cost of Investing is the hub on marketing tactics and a red-flag checklist for evaluating any product.
• Most Stocks Lose to T-Bills covers the Bessembinder structural reason most concentrated active strategies underperform: only ~4% of stocks drive the market, and narrow portfolios mathematically miss them.
• Fama-French Factor Analysis is the framework for understanding what drives your “passive” portfolio’s returns.
• The Case for Small-Cap Value covers the academic evidence behind systematic factor tilts.
• Why I Like AVUV, AVDV, and AVGV covers systematic active funds that make the discretion explicit.
• The Tech Bro Portfolio shows why owning multiple “passive” ETFs does not guarantee diversification.
• Should You Buy IPO Stocks? covers how IPO inclusion mechanics turn “passive” index buying into systematic post-IPO demand, with measurable shadow-tax cost.