The Dunning-Kruger Effect and Educating Clients

Everyone providing pruning or removal quotes has come across this situation. You pull up to the next appointment at a house in a well-wooded neighborhood. The homeowner greets you with slight disdain as you meet at the door. You walk together through the house and exit through the sliding door into the backyard, which is filled with a single large tree.

People with low skills and knowledge of a task often overestimate their ability to accomplish it. TCIA graphic.
People with low skills and knowledge of a task often overestimate their ability to accomplish it. TCIA graphic.

The tree is a majestic American elm. It has the classic vase-shaped form of this species, with a high crown that shelters the entire backyard within its shade. The branches at the edge of the canopy bow gracefully down, almost touching the tall fence surrounding the property. Too bad the elm finally succumbed to Dutch elm disease, having survived decades beyond its peers.

You stand there quietly calculating the hours of climbing – no lift access for this one – and the rigging that is necessary to safely bring the tree to ground. While you scan the tree, the homeowner turns to say, “I know I can do this tree myself. I spend a lot of time in deer stands, so I do not mind heights. I can get it down in an afternoon with a couple of friends.”

“So, why am I here?” you wonder.

“I figured I would let some tree guys do it,” the homeowner continues, “since I am not sure what to do with all the brush.”

There it is. Your company is not being hired for the knowledge and skills to do this complex work. No, it is as a trash-hauling service. Too often our work is reduced to this level of simplicity. Anyone can do it if you can rent the right equipment or have a place to dump the brush. Homeowners masquerading as arborists are a good example of the Dunning-Kruger effect.

Training – in addition to the right tools and proper PP
Training – in addition to the right tools and proper PPE – separates tree workers from homeowners. Photo courtesy of Kramer Tree Specialists Inc.

The Dunning-Kruger effect

The Dunning-Kruger effect was first published about two decades ago. There are some limitations to this research, and it has been subject to criticism. It even received an Ig Nobel Prize – a pun on the Nobel Prize – for unusual, imaginative or trivial research. But the central theme of the study holds true. It is that people with low skills and knowledge of a task often overestimate their ability to accomplish it. They may have watched someone perform the task, or more likely watched it on YouTube. The task looked easy to do.

A good example of the Dunning-Kruger effect is the results of a recent survey from Griffith University that found half the male respondents were confident they could land a commercial jet. There have been instances when a passenger with little to no pilot experience landed a small, single-engine aircraft – with coaching – when the pilot was incapacitated. A passenger with no flight training and experience safely landing a Boeing 737 to the cheers of their fellow passengers is for the movies. The odds are next to zero.

The combination of ignorance and overconfidence in a person’s ability to complete a high-risk task can lead to a dangerous situation. This happens when tree owners attempt to be arborists. Over the past three years, TCI Magazine published a series of “Us Versus Them” articles contrasting incidents between homeowners and arborists in their use of chain saws, chippers, ladders and aerial-lift devices during arboricultural operations. It is time for an update. (See the June 2023 issue of TCI for the previous most recent “Us Versus Them” article and a guide to the series.)

The evidence

There are about 140 million visits to the emergency department (ED) every year. Most patients are treated and released the same day, but about 14% are admitted to the hospital. Upper respiratory infections are the most common reason for an ED visit, followed by superficial injuries and nonspecific chest pain. Open wounds – injuries commonly associated with tree work – are the seventh most-common reason for a visit.

Chain saws are one of the most basic tools we share with homeowners. But arborists are required to wear personal protective equipment – helmet, hearing protection, eye protection, sturdy footwear and cut-resistant leg protection (for ground operations with a chain saw). Tree owners wear ball caps, shorts and flip-flops. Arborists must follow OSHA regulations and the ANSI Z133 standards for operating chain saws. Tree owners merely need to pick up a couple of tips from YouTube.

The casual attitude tree owners have toward chain saws is mystifying. They understand the power of the chain to plane through wood, but somehow do not equate this with their flesh. They also have extraordinary confidence in their skills at saw work. When asked about the absence of PPE, a common response is, “Why do I need it? I am not planning to have an accident.”

Several years ago, when a derecho swept across eastern South Dakota, I and many other arborists quickly began the task of removing fallen trees from buildings, cars and roadways. The local big box hardware store sold out of chain saws in a day. Removing twisted and bent trees lying on houses is not the best place to start learning how to operate a chain saw. There were several fatal incidents.

Arborists have to follow OSHA regulations and the ANSI Z133 standards for operating chain saws. Homeowners masquerading as arborists do not.
Arborists have to follow OSHA regulations and the ANSI Z133 standards for operating chain saws. Homeowners masquerading as arborists do not. Photo courtesy of Andy Jones, CTSP, Rooted Arbor Care.

Numbers don’t lie

Unfortunately, tree owners’ high confidence in their skills is not aligned with a low incident rate. During the past three years, there have been about 77,000 ED visits associated with chain saws. About 91% of these incidents involved the public, the tree owners. The rest were workers operating chain saws as part of their profession – loggers, landscapers, grounds-maintenance workers, site contractors and, of course, arborists. This is a slight increase from the 2010s. Why there was an increase in these ED visits is unknown, but I suspect it is related to the pandemic.

There is a lot to remember about the COVID pandemic. The tragic loss of lives is the most important, but there were and are numerous other effects. One was that everyone was home, and the second was that money – for many – was still coming in and supplemented by government checks. This combination of being homebodies and having surplus income meant homeowners were interested in home improvements, especially landscaping, patios, decks and tree care. Nearly every tree service was swamped with work in 2020 and 2021. Many homeowners also decided to do tree work themselves. This meant they were using chain saws.

What they cut

The average age of someone arriving at the ED from a chain-saw incident in that three-year period was 47 years old, with a range from 6 to 91 years old. The incidents involving children were usually tripping and falling on a chain saw that was not running. There were, however, incidents involving 9-, 10-, 11- and 12-year-olds who were injured from operating chain saws. About 87% of the injuries occurred to males.

The most common injury presented to the ED was laceration to the thigh, typically the left leg – about a quarter of the incidents. About another quarter of the incidents were lacerations to the knee, ankle or foot. About 10,000 incidents a year involved hospitalization, all deep lacerations. But about 50 hospitalizations each year involved amputations, mostly left fingers or thumbs.

Trimmers and pruners

Fingers also were cut or lost to hedge trimmers and pruners. There were about 3,600 of those visits to the ED each of the past three years. The average age was 50 years old but ranged from 10 to 87 years old. Nearly all the incidents involved fingers. These occurred when someone was operating the equipment one handed.

Chippers and shredders

Chippers and chain saws go hand in hand for arboricultural operations, and increasingly so for tree owners. Smaller chippers and shredders can be rented by tree owners with minimal to no training. It shows.

There were about 1,400 emergency-department visits associated with chippers and shredders, again a slight increase from the 2010s. About 79% of these incidents were to tree owners, usually operating the smaller chippers, shredders and mulchers.

Arborists, loggers, site-cleaning contractors and other professionals use larger chippers. Operator injuries while working with these larger machines were more serious and often fatal. Tree owners who used these larger machines also suffered amputations of legs and arms.

Overall, about 88% of the chipper injuries occurred to males.

The average age of someone arriving at the ED from a chipper/shredder incident was 45 years old, with a range from 3 to 86 years old. About 12% of these ED visits were to patients under 18 years old. The chipper-related injuries to children were not to operators, but observers who were struck by branches that were being fed into the machine.

There were injuries to minor teens operating chippers at home. Unfortunately, injuries to minors also occurred on commercial tree crews, including one fatality when a 17-year-old became entangled in the brush and was pulled into the machine.

The most common chipper injuries presented to emergency departments were lacerations or amputations of fingers. This happened when the hand was caught between the brush and the chipper shroud when the wood violently kicked to the side. Wood that kicked back or to the side while being fed was responsible for scalp lacerations, abrasions to the face and chest injuries.

Grinders and splitters

Two other pieces of equipment that resulted in injuries were stump grinders and wood splitters. The stump-grinder injuries were finger or thumb amputations and lacerations. These occurred when the operator touched the teeth while pulling debris off the wheel. The wood-splitter incidents were amputations or lacerations from the fingers caught between the log and the splitter wedge.

Ladders and lifts

Rib and spinal fractures were injuries associated with pruning trees from a ladder. All the falls were less than 30 feet, most less than 10 feet. Falling from the ladder resulted in cervical, pelvic and rib fractures.

Electrical-shock injuries also were associated with ladders and falls. Tree owners directly contacted an overhead power line through a metal pole pruner or, in a few incidents, touched the power line with the ladder as it was being moved into position.

Aerial devices are another common piece of equipment rented by tree owners. Tree owners fall from aerial devices for the same reason arborists do – failure to wear fall protection. The difference is that if someone is renting a lift, the unit typically does not come with a fall-arrest harness, or it is optional.

Homeowners rent units that can reach 50 to 70 feet. The internet is populated by descriptions of saving thousands of dollars by do-it-yourself tree dismantling. Many of the falls were from overreaching while pruning with a chain saw and tumbling out of the basket.

Tree workers, whether on the ground or in the tree, are trained in the potential hazards and proper PPE.
Tree workers, whether on the ground or in the tree, are trained in the potential hazards and proper PPE. Photo courtesy of Kramer Tree Specialists Inc.

Then there’s the tree

While operating equipment poses significant risk to the amateur tree worker, the tree is also a hazard. The two greatest hazards are being struck by a falling branch or by a falling tree. Emergency-
department visits are weighed more heavily toward falling branches than falling trees. Being struck by a 10-ton tree as it falls does not usually call for emergency medical personnel – more often the coroner.

Tragically, every year amateur tree fellers or bystanders are killed by a falling tree. These are usually from misjudging the tree’s height or direction of fall. Fatal injuries also occurred to amateurs when trees split during felling.

The average age of the tree owners coming to an ED after a fight with a tree was 53 years old. The ages ranged from 14 to 92 years old. The most common incident was a branch striking the tree owner as they were cutting the branch or completing the cut. The tree owners were standing below the branch, sometimes on a ladder, and were hit by the falling or swinging branch.

Another common occurrence was during limbing and bucking the fallen tree. A partial cut branch swinging back and striking the chain-saw-operator’s chest caused rib fractures. Sometimes these cause pneumothorax, a punctured lung.

Head and eye injuries

Not too surprisingly, head injuries are another common injury from removals and pruning. These ranged from concussions to skull fractures. Scalp lacerations were the most often treated, along with nose bleeds.

Another injury was corneal abrasions – an injury to the eye – though sometimes it was the more serious orbit fracture (damage to the bone around the eye). A common factor in these incidents was the lack of PPE. While arborists routinely wear a helmet and eye protection, the best that most amateur tree workers might wear is a ball cap and sunglasses.

Climbing injuries

Tree owners also tried their hand at climbing. This was climbing without fall protection, usually just climbing off a ladder onto the branches. The falls were not from great heights. Most falls were between 10 and 25 feet.

But falls from trees, whether as a professional or amateur, rarely are a straight fall to the ground. Instead, the falling climber frequently ricochets through the canopy on their way down or strikes objects on the ground, such as fences. The common injuries were fractures, lacerations and punctures.


The Dunning-Kruger effect also shows that once people understand the complexity of a task and its risks, they are less likely to be confident in their ability to perform it. The tree care industry must continue to educate tree owners in the difficulty of performing arboricultural operations – and the consequences of attempting to perform high-risk tree work.

If the discomfort and pain of an injury is not enough to cause hesitation, then the thousands of dollars of medical care and lost time is higher than the charge from any tree service to do the job.

John Ball, Ph.D., BCMA, CTSP, A-NREMT (Advanced-National Registry of Emergency Medical Technicians), is a professor of forestry at South Dakota State University.

1 Comment

  1. Thank you for this article, Dr. Ball. A bit of humor helps make the humble pill go down. Please continue to do the great work that you do.

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