VALID's Risk Assessment Model
We're at the end of another successful tree risk training and advisory tour of NZ & AU. On this trip, we've been told some Aussie Arborists are not yet sure about upgrading their approach to tree risk with VALID because of a point raised in Peter Gray's Tree Risk Assessment Review for Arboriculture Australia's 'The Bark' magazine (2020).
Advantages & Disadvantages
In the article, Peter suggests a disadvantage of VALID is:
"The underlying mathematics running the App have not been made available for peer review. VALID claims to have used the services of a respected and independent maths professor to develop and test the App but this must be accepted without any chance to review and criticise it."
This 'disadvantage', is in fact an 'advantage'.
Our Risk Professor
First, the 'Maths Professor' is in fact a 'Risk Professor'.
He's Professor Willy Aspinall. Willy is the Cabot Professor in Natural Hazards & Risk Science at Bristol University, and he said this about the 'underlying maths'.
"We have stress-tested VALID and didn't find any gross, critical sensitivities.In short, the mathematical basis of your approach is sufficiently robust and dependable for any practical purpose."
VALID is the only tree risk system that's been put together with a Risk Professor, who's an internationally distinguished expert in assessing risk in the natural environment. Surely, this is an 'advantage', and not a 'disadvantage'.
3 points about making the 'underlying maths' available.
1) It would give away our intellectual property, and anyone could copy it. Similarly, Google doesn't make its search algorithm available.
2) We're planning to write a paper with the Professor once he's less busy being an expert witness on the risk to Japanese nuclear reactors from an Aso volcano super-eruption .
Or on the fallout from the New Zealand Whakaari/White Island volcanic eruption.
3) How the matrices are constructed in TRAQ is not available for peer review. Neither are the Monte Carlo simulations in QTRA available for peer review.
Another consideration is, the underlying maths won't help a Duty Holder or Risk Assessor with their decision-making. Indeed, some might think they know better and try to numberwang the model to game the risk they want.
We were also told, some Duty Holders and Arborists are concerned about how they would explain their decision making if they ended up in court.
If you use VALID, it's extremely unlikely you'll end up in court. If you did, as long as you don't make a green decision when it should be red - which is incredibly difficult to do - we've got your back.
The Bolitho Test
Taking the Defect Out of Tree Risk - Article Update
'Taking the Defect Out of Tree Risk' is published in the current NZArb 'Tree Matters' magazine.
It first appeared in the UK's Arboricultural Association's (AA) Arb Magazine (Spring 2001).
There are a couple of important improvements in the latest version.
Like the Obvious Tree Risk Features Guide, which now includes construction damage.
We've also improved the VALID Likelihood of Failure mnemonic to prepare for v2 our Tree Risk App. In our excitement about dumping the red DEFECT and replacing it with the neutral DECAY in the AA version, we neglected how this affected some subheadings.
Tree Defects & Hazards v Features & Benefits
Any assessment of risk from trees falling should begin with a Tree Risk-Benefit Management Strategy.
Whether you're a Duty Holder or a Risk Assessor, here are 5 valid reasons why the Strategy is your greatest tree risk asset.
1 The Context
A Strategy establishes the context (ISO 31000) of the risk universe in which you're working, sets out your stall, and defines the rules of the game.
2 What you're doing
It makes it clear what a Risk Assessor is doing when they're looking at a tree, why they're doing it, and what the limitations are.
3 The donkey work
The Strategy does more than 95% of your risk assessments for you.
Your insurers will be happy to underwrite you.
5 The truth of the matter
The Strategy 'speaks truth to power'.
speaking truth to power
In the extremely unlikely event of an Acceptable or Tolerable risk happening. And a claim is being considered. It's the Strategy that puts you in the best position to disarm an Expert Witness who struggle with risk literacy. Or regulate a Risk Entrepreneur, who profits by talking up the risk.
The Strategy also gives you defence in depth by speaking truth to Judges, Coroners, and Enforcement Officers.
If you want to know what a Tree Risk-Benefit Management Strategy looks like, we've got a whole bunch of free templates on our Risk Management page.
We know from pedestrian data, the centre of built-up areas have a Likelihood of Occupancy that's so high, on average more than one person is exposed to the risk.
Occupancy is Very High.
We also know from traffic data, the busiest roads have a Likelihood of Occupancy that's so high, on average more than one vehicle is exposed to the risk.
Where we have busy roads next to busy footpaths in towns and cities, we know the combined occupancy of people AND traffic is so high, on average more than one person AND one vehicle is exposed to the risk.
We know other tree risk assessment systems systematically undervalue Very High Occupancy. From the training we’ve delivered, we also know tree risk assessors have been poorly trained to recognise both Very High and High Occupancy.
What all this means is unless you’re using VALID, and have had Likelihood of Occupancy training (it’s really easy once you're calibrated), you’ll be undervaluing the occupancy where it matters most.
If you're undervaluing the occupancy, you'll be undervaluing the risk.
You’ll be undervaluing the risk by at least a whopping factor of x10 or x100.
A 1:1M risk might be as high as 1:10K.
A Low Risk might be a High Risk.
If you've heard of Daniel Kahneman, you'll likely have read his excellent Thinking Fast & Slow, where he shares his Nobel Prize winning work into behavioural economics. All that fascinating stuff about how ingrained biases often have reasonably foreseeable impacts on our decision making.
His most recent interest has been a collaboration with Oliver Sibony and Cass Sunstein, exploring the role of 'Noise' in decision making.
Noise is the significant variability in decisions you get where there shouldn't be any. Such as when Doctors diagnose disease, or when Judges sentence criminals.
Or when Arborists make tree risk assessment decisions.
Earlier this year, More or Less' Tim Harford had a short chat with Daniel Kahneman about how to reduce Noise by practising Decision Hygiene.
If you want to dive into the Decision Hygiene part, it starts at 5.50.
What was eye-opening about this discussion into the benefits of practising Decision Hygiene is that it's embedded in VALID.
Arborists' tree risk assessments are notoriously noisy. Ask 10 Arborists to risk assess a tree and you'll likely get 12 very different decisions.
One of VALID's benefits is we've designed it to reduce this Noise. When it comes to Occupancy and Consequences, consistent and good decision making is so 'quiet' you don't need to be an Arborist to do it well.
In tree risk assessments, we get most Noise with Likelihood of Failure decisions.
When you make your Likelihood of Failure decision in VALID, you're guided to evaluate all the likelihood of failure attributes, independently of each other, before you make a decision.
This VALID approach to Likelihood of Failure decision making is what Daniel Kahneman is calling Decision Hygiene.
Whilst rummaging through some of the UK's dusty Risk & Regulation Advisory Council archives, we strayed across 'A Worrier's Guide to Risk'. David Spiegelhalter (Chair of the Winton Centre for Risk and Evidence Communication at the University of Cambridge) put it together for them in the noughties.
It's a great guide to thinking about risk, some of which applies to trees, on one side of paper - our favourite length for a subject.
We're now into a prolonged hot dry spell of weather. When this happens, anxious Duty Holders often get in touch about managing the risk from Summer Branch Drop (SBD), or Summer Limb Drop (SLD), or Sudden Branch Drop (SBD), or Sudden Limb Drop (SLD).
What to do?
The uncertainty about what to call SBD, or SLD, is often matched by similar uncertainty about how you should manage the risk.
Should you put up signs?
Fence trees off?
Fact-checking the risk
The overall risk from SBD is mind-bogglingly low.
From the data, the risk is so low, our risk of death from driving for the few minutes it takes to cover about 5km/3mi is higher than from SBD over a whole year.
Finding a microscopic straw-coloured needle in a gargantuan haystack
Despite this mind-bogglingly low risk, fear-mongering from Risk Entrepreneurs*, claiming legal action is likely if the risk were to happen and it wasn't managed or assessed, has had some anxious duty holders putting up confusing and ineffective signs.
Is standing, lollygagging, or laying down fine?
What we know
We know the overall level of risk from SBD is so low it's Acceptable.
We also know, Arborists can't tell the difference between branches that have a high likelihood of failure from SBD, and those that have a low likelihood of failure.
That means, warning signs make no measurable reduction to a risk that's already Acceptable. In fact, the costs of commissioning and managing these signs are grossly disproportionate to any claimed reduction in the risk.
Linger near trees at your peril
Photo Credit - Paul Barton
Exposing yourself in public
Worse still, the ineffectiveness of these signs may backfire and create an opportunity for a Risk Entrepreneur to act as an expert witness in the extremely unlikely event of someone being killed or injured by SBD. It'd be all too easy for them to claim you hadn't managed the risk well enough, and you could've done more.
Why didn't you put up more signs?
Why didn't you fence the tree off?
Why didn't you prune the tree?
Or, if the visitor wasn't an English speaker, why didn't you translate the sign into other common languages?
If you're a Duty Holder, or advise one, worry not. We've got your back on this one with our Summer Branch Drop Guide.
An antidote to risk entrepreneurs
In short, you don't need to do anything to manage the risk unless you have a repeat offender.
We've also got a whole range of guidance of our Risk Management page.
"Treecare professionals who thrive on maximising the perception of risk in order to create standards for which they are perfectly placed to provide profitable solutions."
Rick Haythornthwaite, Risk & Regulation Advisory Council
This is the one-side-of-paper Summary of our Tree Risk-Benefit Management Strategies.
We were first asked to put this together by the Department of State Growth, Tasmanian Government, when they were adopting VALID. It's role was to explain what the Strategy is all about to the departments strategic decision makers. The Summary proved such a useful communication tool, it found its way into the Government Agency template, and we've released it for general use.
How to use the Strategy Summary
It works at two levels. If you're a Duty Holder, you can grasp the complete Strategy within the time it takes to take a few sips of tea or coffee. Similarly, if you're an Arborist you can quickly catch the eye of a busy potential client and add value to your service.
Active Assessment - Every 5 years?
We think a 5 yearly Active Assessment frequency in Zones of High Confluence is reasonable, proportionate, and reasonably practicable. It's what many Duty Holders are adopting. Here, there's strength in numbers singing from the same hymn sheet if a risk is realised and a claim or enforcement action is being threatened. However, this is a Duty Holders decision. If they have a lower 'risk appetite' and are prepared to spend more money, we don't have a problem with a shorter frequency of Active Assessment. Just edit the PDF or Word Template.
Strategy Summary v8.0.pdf
Strategy Summary v8.0.dotx
Here are the main fonts used in the Tree Risk-Benefit Management Strategies.
Source Sans Pro
Georgia is the body text and that should already be on your computer.
We have several free Tree Risk-Benefit Management Strategy templates that we've released under a creative commons licence.
You can read all about them on our Risk Management page, and download them as pdf files.
We're happy to share them with you as Word Template .dotx files as well, which makes it easier to customise the few sections that you need to. We've included the fonts that you might not have.
The is the version for a Homeowner. It's the simplest with a Policy and management by Passive Assessment; which is keeping an eye out for Obvious Tree Risk Features you can't help but notice.
Homeowner TRBM Strategy v8.0.pdf
Homeowner TRBM Strategy v8.0.dotx
The is the version for a School, College, or University. It's similar to the Landowner one, where the Duty Holder has no trained Arborists as staff.
School TRBM Strategy v8.0.pdf
School TRBM Strategy v8.0.dotx
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