Human Variability
Human variability recognizes that people's behavior naturally differs, enabling creativity, innovation, and adaptation. It suggests that deviations from standard procedures are not necessarily errors and can be crucial for safety and success.
THE IDEA
Human Variability and ‘the Miracle on the Hudson’
Recent developments in systems thinking have now broadened the focus from human error to consider human variability. The argument is that most people try to do their best most of the time, but what they do can vary depending on the situation. Human variability accepts that people are not the same as clones or robots. It says that without human variability, we would have no creativity, innovation and adaptation as the situation requires. In other words, human variability is sometimes a part of what we must do to keep things safe. Not every variation in behaviour can be pre‐judged as being definitively an error.5
A notable illustration of human variability in action can be found in Flight US 1549 in January 2009. A flock of Canada geese damaged the plane's engines shortly after take‐off from the LaGuardia airport, New York City, and Captain Chesley (Sully) Sullenberger made an ‘in the moment’ and far from obvious decision (and contrary to air traffic control advice) to land the aircraft in the Hudson River, enabling all the passengers and crew to evacuate with no loss of life and few injuries. This was nicknamed ‘the Miracle on the Hudson’.6
In the extensive air crash investigation led by the US National Transportation Safety Board (NTSB), numerous attempts to recreate the conditions he faced in flight simulators showed how ‘Sully's’ decision was almost the only choice that could have avoided a catastrophe.7 In the end, many honoured him for his incredible judgement and skill, especially following such an unexpected and shocking event, with so little time to decide what to do, followed by a nearly flawless landing on water.
A human variability mindset recognises that some people can excel in challenging situations and tough times. Still, it also acknowledges that heroic or superhuman efforts aren't something we can bank on. Many of us, much of the time, will try to do our best, even if that means a slight deviation from what the official procedures require because of time constraints or other factors. But that doesn't mean we will always get things right. Variability is a fact of life we must recognise, and if we don't want any deviation from a pre‐determined formula, this is where an automated procedure may be called for (albeit that it may come with its own problems).8
When to use it
In high-stakes environments like aviation, where pilots must make rapid decisions based on changing circumstances.
In healthcare, where doctors and nurses adapt protocols to patient-specific needs.
In product design, where user variability requires flexible interfaces.
In crisis management, where standard procedures may need to be overridden for survival.
FROM THEORY TO EVERYDAY LIFE
In practice
The Miracle on the Hudson
In January 2009, US Airways Flight 1549 lost power in both engines after striking a flock of Canada geese shortly after takeoff from LaGuardia Airport. Captain Chesley Sullenberger made the quick decision to land the aircraft in the Hudson River, contrary to air traffic control advice. All 155 passengers and crew survived. The NTSB investigation showed through simulations that Sullenberger's decision was nearly the only viable option to avoid catastrophe. This event illustrates how human variability—the ability to adapt and make non-standard decisions—can lead to exceptional outcomes in critical situations.
A MOMENT TO REFLECT
Put it to work.
How can we design systems that account for natural human variability rather than demanding rigid adherence to procedures?
When is a deviation from standard procedure a sign of error versus a sign of adaptation?
How can we foster an environment where human variability is recognized as a strength in safety-critical situations?
Often confused with
CONTINUE THE CONVERSATION
Source texts
- Beyond the Five Whys Root Cause Analysis and Systems Thinking (James C. Paterson)