The Hidden Driver of Factor Outperformance: Company Size
Let’s be clear upfront: factor investing absolutely matters. However, when you apply a factor screen, you are typically reweighting securities based on those specific characteristics rather than their raw market capitalization. Over the last decade, as mega-cap stocks have relentlessly driven broad market returns, this structural shift away from market-cap weighting has created a massive hurdle for traditional factor strategies.
The core dynamic is straightforward. When the absolute largest companies in the benchmark are the top performers, it becomes next to impossible for any strategy to keep pace—let alone outperform—unless it holds those mega-caps in at least an equal weight to the parent index. But what happens when that decade-long mega-cap dominance takes a breather?
Looking at popular S&P 500 factor ETFs year-to-date, we can see a striking trend. All but two of these factor strategies are currently outperforming the broad-market SPY—in many cases, by a wide margin. When we look under the hood to find the common thread, market capitalization stands out glaringly. Furthermore, while lower valuations (P/E) have certainly provided a tailwind for value-oriented funds, the implementation method—specifically how these funds weight their constituents—reveals that moving away from market-cap weighting is the real engine of this size shift.
| Ticker | Fund Name | Implementation | YTD TR % | Top 10% | Wtd. Avg. Market Cap ($M) | P/E (NTM) |
|---|---|---|---|---|---|---|
| SPYD | State Street SPDR Portfolio S&P 500 High Dividend ETF | Equal Weighted | 10.96 | 13.95 | 49,271 | 14.81 |
| SPHD | Invesco S&P 500 High Dividend Low Volatility ETF | Scored | 10.14 | 28.74 | 68,734 | 13.96 |
| NOBL | ProShares S&P 500 Dividend Aristocrats ETF | Equal Weighted | 10.11 | 16.04 | 118,723 | 19.19 |
| QVMT | Invesco S&P 500 Concentrated QVM ETF | Scored | 8.99 | 42.09 | 477,920 | 19.70 |
| SPLV | Invesco S&P 500 Low Volatility ETF | Scored | 8.77 | 12.77 | 101,820 | 21.59 |
| RPV | Invesco S&P 500 Pure Value ETF | Scored | 8.74 | 19.24 | 48,157 | 12.12 |
| SPHQ | Invesco S&P 500 Quality ETF | Scored | 7.85 | 40.74 | 390,088 | 22.10 |
| RSP | Invesco S&P 500 Equal Weight ETF | Equal Weighted | 7.00 | 3.20 | 120,513 | 18.01 |
| RPG | Invesco S&P 500 Pure Growth ETF | Scored | 6.76 | 27.00 | 374,861 | 23.01 |
| SPVM | Invesco S&P 500 Value with Momentum ETF | Scored | 6.38 | 31.26 | 128,820 | 14.15 |
| RWL | Invesco S&P 500 Revenue ETF | Revenue | 5.74 | 23.44 | 523,776 | 17.13 |
| SPHB | Invesco S&P 500 High Beta ETF | Scored | 5.24 | 14.06 | 229,319 | 18.51 |
| SPYV | State Street SPDR Portfolio S&P 500 Value ETF | Market Cap | 4.74 | 22.72 | 534,522 | 19.19 |
| SPY | State Street SPDR S&P 500 ETF (Benchmark) | Market Cap | 0.60 | 36.42 | 1,277,688 | 21.38 |
| SPMO | Invesco S&P 500 Momentum ETF | Scored | 0.13 | 50.59 | 866,789 | 21.74 |
| SPYG | State Street SPDR Portfolio S&P 500 Growth ETF | Market Cap | -2.93 | 59.89 | 1,972,131 | 24.00 |
The Mega-Cap Drag
Notice the bottom of the table. The benchmark (SPY) is barely positive at 0.60%, sporting a massive weighted average market cap of over $1.27 Trillion. The only two funds underperforming or barely keeping pace are Momentum (SPMO) and Growth (SPYG). They both carry staggering average market caps of $866 Billion and $1.97 Trillion, respectively, driven heavily by their reliance on market-cap weighting or implementation approaches that mimic those constraints.
Valuation vs. Size
Conversely, look at the top performers. While funds like SPYD, SPHD, and RPV do sport attractive NTM P/E ratios (under 15x), their defining trait isn’t just cheapness—it’s their implementation. By using Equal Weighted or Scored methodologies, they forcefully break the market-cap mold, resulting in vastly lower average market caps between $48 Billion and $68 Billion.
To truly drive this point home, consider the historical relationship between the S&P 500 Equal Weight ETF (RSP) and the standard market-cap weighted SPY. The chart below clearly illustrates the inflection point: as the weight of the top 10% of SPY constituents began its dramatic ascent, market-cap weighting’s outperformance accelerated in tandem.
My point here is not to suggest that factors don’t matter. They certainly do. Rather, the data illustrates a structural reality: when a strategy weights securities by factor traits instead of size, it inherently dilutes its exposure to the market’s largest names. If the size factor is running hot—as it has for the better part of a decade—you can generally forget about a factor strategy keeping up with the broad benchmark unless that strategy also happens to heavily overweight those same mega-cap leaders. When evaluating factor strategies, recognizing how far a portfolio deviates from the mega-cap concentration of the core benchmark is essential for setting realistic performance expectations.
