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Size Really Does Matter

Size Really Does Matter

Smart Thinking: A Skill Versus Luck Essay Series | Issue 8

Written by Michael A. Ervolini

Size Really Does Matter

INTRODUCTION

Position Sizing is a crucial fund manager skill. It determines if the alpha from great buys is effectively harvested and if questionable purchases are restricted in the damage they inflict. Alternatively, chronically underweighting the strongest positions and overweighting the weakest holdings is a headwind if not a surefire path to underperformance. While the asset management industry expends vast amounts of time and energy discussing this activity surprisingly little is known about which managers size positions effectively, which don’t, and how to tell them apart. Fortunately, this situation is changing for the better. The improvement is due to the growing number of firms providing decision-based skill analytics.[1]

POSITION SIZING

One such firm is Alpha Theory. They are laser focused on position sizing. This includes quantification of a manager’s sizing skill, helping managers improve their sizing processes for greater alpha capture, and supporting asset owners/investors in assessing a manager’s sizing acumen. Alpha Theory has analyzed well over 200 equity funds involving more than 14 years of historical data. Their research indicates far more sizing opportunity than success currently, as they relate in their 2025 Year In Review: “Active sizing, the activity managers devote enormous amounts of energy to, reduces returns on average in our dataset.” [2] Specifically, they have uncovered: “Across the past 14 years, the Optimal portfolio has outperformed Actual by an average of +3.9% annualized.” Alpha Theory attributes the lost opportunity to process shortfalls: “The result is a persistent gap between research conviction and capital allocation.”

The way Alpha Theory computes its results is to compare a fund’s actual returns to a counterfactual portfolio in which positions are sized optimally based on Alpha Theory’s proprietary analytics. The latter approach is referred to as “optimum position sizing.” In constructing the counterfactual portfolio Alpha Theory uses all of the manager’s actual decisions of when to buy (open a position) and sell (close a position). Alpha Theory then adjusts how positions are sized to take full advantage of all the information available to the manager. As they describe it: “The Optimal portfolio is not an outside model or black box optimizer. Instead, it’s the manager’s own price targets, probabilities, conviction levels, and risk constraints applied consistently and without the behavioral noise that creeps into day-to-day sizing decisions.” This method assures that the counterfactual constructed reflects realistic and achievable sizing levels bespoke to each fund.

The Alpha Theory research indicates that the results are persistent over time as well. Their report states: “On average, the Optimal portfolio has outperformed Actual in 13 of 14 years — a 93%-win rate.” Interestingly the research shows that higher success is mostly about doing better at the margins: “By Position: Optimal sizing wins 57% of the time — a modest edge per position, but powerful at scale.” This finding underscores the importance of both having an effective process and actually adhering to it.

UPSHOT

Achieving benchmark-beating results is difficult. Doing so requires that each skill is well understood, contributing positively to alpha, and is likely to continue doing so going forward. The work done by Alpha Theory enables asset owners and allocators to formulate a deeper understanding of how well the manager is capitalizing on their best buys. With 4% hanging in the wings this type of analysis is invaluable.

CONCLUSION

Position sizing can be either a source of incremental alpha or a risk factor. Developing and then relying upon a sound sizing process is what makes the difference, according to research from Alpha Theory. Their findings are confirmed by other decision-based analytics investigations.[3] Interestingly, Alpha Theory found that on average the funds studied would have performed better even if the positions were equally weighted. However, managers can do much better than this they encourage: “The solution is not to abandon sizing, but to structure it. In our dataset, when those same research insights are applied through a disciplined sizing framework, they outperform equal weight by an additional 2.2%. That is the real advantage: not better stock selection, but better alignment between capital and conviction.”

Decision-based analytics such as those provided by Alpha Theory are substantially improving the industry’s understanding of manager skill. These newer analytics can rigorously quantify individual skills like sizing and compute its consistency. This information supports stronger allocation decisions and enables fund managers to become more self-aware and improve.

ENDNOTES

  1. Michael A. Ervolini, Skill Versus Luck: Taking The Guessing Out Of Equity Fund Selection, MIT Press, February 2026, Chapter Three.
  2. Cameron Hight and Justin Olson, “Alpha Theory 2025 Year in Review: Position Sizing as a Persistent Edge.” The full text is available at: https://www.alphatheory.com/blog/alpha-theory-2025-year-in-review-position-sizing-as-a-persistent-edge
  3. Michael A. Ervolini, Skill Versus Luck: Taking The Guessing Out Of Equity Fund Selection, MIT Press, February 2026, Chapter Thirteen.
Michael Ervolini headshot

MICHAEL A. ERVOLINI, AUTHOR

The ideas expressed on this website are developed and/or curated by Michael Ervolini. Mike has spent his entire 35 year + career leading efforts to improve and strengthen active management.

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Essays

Counterfactual Investing

Behavioral Matters: Insights from the application of Behavioral Finance | Issue 14

Written by Michael A. Ervolini

Counterfactual Investing

“So we have the paradox of a man shamed to death because he is only the second pugilist or the second oarsman in the world. That he is able to beat the whole population of the globe minus one is nothing; he has “pitted” himself to beat that one; and as long as he doesn’t do that nothing else counts.”

– William James

INTRODUCTION

Imagination and creativity help turn good ideas into winning strategies and great picks if they are calibrated to ensure favorable results. Imagination also can push investors toward unproductive decisions — ones that feel right while lowering performance. Known as Counterfactual Thinking, this type of deliberation can affect your interpretation of results and can shape the buys and sells you make.

DARN, I JUST MISSED IT

Emotional responses to outcomes often are influenced by what might have been. Counterfactual Thinking, as such thoughts are known, often ends in regret. The emotional response to an event depends on how easily one can conjure up alternate outcomes that are either better or worse. An often cited example regards missing a flight by five minutes or 45 minutes. People that just miss their flight tend to kick themselves more than those who missed their plane by a mile. The closer you were to making the flight, the easier it is to construct an alternative outcome or counterfactual that triggers regret.

WHEN WORSE IS BETTER

Who should be happier, the person that wins the silver medal or the bronze? The silver medal winner is objectively better off — he or she is closer to gold than the bronze medal winner. Yet, that is precisely why a silver medalist enjoys second place far less than the bronze medalist enjoys coming in third.

In analyzing medal winners from both the Olympics and the Empire State Games, researchers Thomas Gilovich, Victoria Husted Medzec and Scott Madey found that silver medalists were less happy with their accomplishment than bronze winners. The silver medalists created a counterfactual based on not having won gold, focusing upward and ruminating about how close they came to first place. This thinking induced feelings of regret and frustration… the, if-only-I-hads. The bronze medalist, in contrast, focused downwards and formulated a more positive counterfactual. Rather than being among the others hitting the showers, they were at least up on the awards pedestal and very happy to be there. Counterfactual Thinking does more than color how we feel about past events; it can also trigger surprising actions.

PHANTOM GAINS AND LOSSES

Investors sometimes generate counterfactuals when they consider repurchasing previously owned stocks. In their paper “Once Burned, Twice Shy” Terrance Odean, Michal Strahilevitz and Brad Barber observed that investors are more likely to repurchase a stock when its current price is below that at which it was sold, and less likely to repurchase it when the current price is higher. The counterfactuals motivating these choices are explained as: “Investors who buy a stock at a lower price than they previously sold it experience the pleasure of knowing they are better off than if they had never sold that stock. Investors who buy a stock at a higher price than they previously sold it are painfully aware that they are worse off than if they had simply never sold that stock.” The terms “knowing” and “being aware“ express the feelings investors have about these purchases based on their if-only-I-hads.

The more relevant question for these investors is whether any stock they previously owned is likely to outperform alternate stocks going forward. For example, repurchasing a stock at a price higher than at what it was sold might be a good investment decision — even though it might feel bad. The counterfactuals make the investor feel a loss or gain based on price movement when the stock wasn’t even owned. This distracts from focusing on today’s thesis and how the stock will perform going forward. The result can be murky judgment — where emotions emanating from if-only’s override objective analysis.

CAN’T WIN FOR LOSING

Counterfactuals also shape the choices made when adding to current positions, according to Odean et al. Investors tend to add less frequently to holdings whose price has gone up, since being purchased (“winners”) and add more frequently to those whose price has dropped (“losers”). The counterfactual created for winners is, “I should have purchased more when it was cheap.” Investors prefer to avoid feeling the regret that this counterfactual brings, so they tend to avoid these buys. The counterfactual for buying losers seems to be associated with avoiding the pain of losing, as in, “If I buy more now and the price moves up, I can regain my current losses.” This counterfactual is consistent with Prospect Theory and resetting one’s reference point. The team’s research demonstrates, however, that the investors were no better off preferentially adding to losers over winners. Feeding their counterfactuals did not enhance their returns.

CONCLUSION

Counterfactual Thinking can hurt performance. It has the power to make silver medalist feel worse than those taking bronze. It can drive investors to make decisions based on if-only’s rather than facts. Counterfactuals can cause you to consider repurchasing stocks based more on price movement since being last sold than on current thesis. They can also cause you to refrain from adding to current portfolio winners… perhaps missing a huge run-up in the bargain. Selfawareness counters such ineffective thinking — keeping decisions factual.

ENDNOTES

  1. “When Less Is More: Counterfactual Thinking and Satisfaction Among Olympic Medalist”, Thomas Gilovich, Victoria Husted Medzec and Scott F. Madey, Journal of Personal and Social Psychology, Volume 69, 1995.
  2. “Once Burned, Twice Shy: How Naïve Learning and Counterfactuals Affect the Repurchase of Stocks Previously Sold”, Terrance Odean, Michal Strahilevitz and Brad M. Barber, Working Paper, September 2004.

MICHAEL A. ERVOLINI, AUTHOR

The ideas expressed on this website are developed and/or curated by Michael Ervolini. Mike has spent his entire 35 year + career leading efforts to improve and strengthen active management.

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When Unconscious Desires Motivate Fund Selection

Journal of Investing | May 2023

Written by Michael A. Ervolini and Andrew R. Tuttle

When Unconscious Desires Motivate Fund Selection: Active Share and Position Count May Do More To Relieve Angst Than Identify Skill

Article Abstract

Identifying equity funds likely to outperform remains a daunting task for capital allocators. Traditional portfolio analyses provide useful insights into how a fund is being managed while offering little clarity on the potential for ongoing success. Active share and position count were introduced as metrics that identify funds that will generate excess returns via skilled management. This paper argues that these metrics provide no information regarding future fund performance or manager skill. It is further proposed that active share and position count do more to relieve unconscious anxiety provoked during the allocation process rather than enhance rigorous judgment.

Three Key Takeaways:

1.

Allocators remain committed to active equities but struggle in identifying skilled managers.

2.

Recent emphasis on high conviction does a poor job at identifying skilled managers. 

3.

Metrics such as active share and position count do more to relieve angst than to support allocation decisions.

MICHAEL A. ERVOLINI, AUTHOR

The ideas expressed on this website are developed and/or curated by Michael Ervolini. Mike has spent his entire 35+ year career leading efforts to improve and strengthen active management.

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