Considering Survivorship Bias in Investing: The Blind Spot That Costs You Money

Dr. Abraham Wald was a Hungarian mathematician who contributed to many fields, but is most noted for founding the field of statistical sequential analysis.  His research years were spent at Columbia University.

During World War II, the Centre for Naval Analyses conducted a study of the damage done to aircraft returning from missions.  Bombing losses were severe and unsustainable.  The study recommended extra armour be added to the areas showing the most damage.

Dr. Wald noted a critical flaw.  The study only considered aircraft that survived their missions.  Every bomber shot down never made it into the damage assessment at all.  The returning aircraft were, by definition, the ones that survived being shot at.  The damage marked areas a bomber could take a hit and still fly home.  It was the untouched areas, the places with no bullet holes in the survivors, that marked where a hit proved fatal.  Reinforce those instead, Wald argued, because the aircraft that took damage there never returned to be counted.  His statistical work for the Applied Mathematics Panel changed how the military approached the problem, and the same reasoning now anchors survivorship bias as a recognised concept across statistics, medicine, and finance.

A Second Story, From the World of Business Books

Thomas James Peters and Robert Hanna Waterman Jr., both McKinsey consultants, published In Search of Excellence in 1982, profiling forty-three companies with strong reputations and financial performance, and distilling eight shared traits behind their success.  The book became one of the most influential management texts ever written.  It also built its entire argument on survivorship bias, in its purest form.  Peters and Waterman studied only the winners.  They never examined the far larger number of companies that shared the identical traits and failed anyway.  Of the thirty-five profiled companies that were publicly traded, fifteen outperformed the overall stock market in the years following publication.  Twenty underperformed it.  A meaningful share of the “excellent” companies studied had, within a handful of years, lost their edge, run into serious financial trouble, or collapsed entirely.  The eight traits were never proven to cause success.  They were simply present in the companies that happened to survive long enough to be studied, exactly the blind spot Wald identified in a very different context four decades earlier.

Why This Blind Spot Applies Directly to Investing

This blind spot applies across many areas of life.  In business and investing, it shows up in otherwise excellent books analysing why certain companies became so successful.  These books rarely consider the far larger number of businesses that shared the same strategy and failed.  The result is a study or report that highlights one slice of the picture while leaving the rest invisible, and that incomplete picture heavily distorts investment strategy.  It is a direct reason investors lose money even in circumstances that appeared, on paper, entirely favourable.

Survivorship bias is especially acute at the small end of the fund market, particularly in impact investing.  Analysis skews toward the success stories, while the far greater number of businesses in the same space that failed simply disappear from the sample.  This makes fund selection feel less like a discipline grounded in evidence and more like a lottery dressed up in due diligence language.  Considering the companies that failed, not merely the ones still standing to be studied, gives a genuinely fuller picture of the actual environment.  It puts an adviser in a stronger position to counsel clients honestly, and to flag structural weaknesses before they turn fatal, rather than reinforcing the same untouched blind spot that once nearly sent Wald's own bombers home with armour bolted to exactly the wrong place.

---

Terence Nunis | Executive Chairman, Equinox Zenith | Author, The 1% Playbook: The Billionaire Cheat Code