Tree Risk Assessment Qualification (TRAQ) – ISA Best Management Practices

[Acer ventura]

Where does the Risk BMP’s risk ranking of Extreme, High, Moderate, and Low for a fatality sit in ToR?

 

 

 

We can see part of the Low risk range for a fatality, but can’t make out where Extreme, High, and Moderate are, so let's zoom in.

 

 

 

Can still only see part of Low risk range for a fatality, which extends off the bottom.

 

Zoom in some more.

 

 

 

Can still only see part of Low risk range for a fatality.

 

Zoom in some more.

 

 

 

Here they are, with the Low risk range for a fatality extending off the bottom.

 

To put what the Risk BMP risk rankings are saying in terms of tangible numbers in relation to say schools, which I opened the thread with.

 

If you have a class of 30 children and a year later 14 of them are dead, this would be ranked as a Low risk.

 

If 29 of the 30 died, this would be ranked as a Moderate risk.

 

By looking at the risk ranking ranges it is also becomes apparent;

 

A Low risk of death can be higher than a Moderate risk of death

 

A Moderate risk of death can be higher than a High risk of death.

 

A High risk of death can be equal to an Extreme risk of death.

 

When I went through this exercise my gut screamed this can’t be right. However, my head can’t come to any other conclusion because that’s what the logic and maths is saying.

 

As I’m sure you can imagine, I’ve gone back over this a number of times and can‘t find fault. It's one of the reasons why I've laboriously and transparently shown the workings out in previous posts, because these risk rankings look like they're a bit of a problem. Can anyone point out where I’ve gone wrong here?

 

As I said in the opening post, one the reasons I've had my sleeves rolled up and been looking at this in so much detail is because of requests about whether QTRA and the Risk BMP can work in tandem from TRAQ accredited arborists and QTRA Registered Users who want to be ISA accredited to assess tree risk. I’ll post the QTRA outcomes in the Risk Matrix tomorrow.

 

Cheers

 

Acer ventura

[Acer ventura]

I'm not sure how it's going to pan out trying to assign any kind of numerical value to these descriptive words but I like the way you are trying to find common ground between both systems.

 

I haven't given this a lot of thought but how about:

 

Imminent = 1/1

Probable = 1/1 – Greater than >1/2

Possible = 1/2 - 1/1000

Improbable = 1/1000 - 1/1000000

 

I'm not very clever (particularly with maths) so hope I haven't contributed utter nonsense!

 

Hi Paul

 

I reckon most things that make you stop and give something a bit of thought, no matter how briefly, are often worthwhile exercises.

 

The main issue with your suggestion of the upper value of ‘Improbable’ being at 1/1 000 would be that with the highest Target value (1/1), and a large tree or very large branch (1/1), we would be looking at a risk of 1/1 000.

 

1/1 000 x 1/1 x 1/1 = 1/1 000

 

A 1/1 000 risk is extremely high by ToR thresholds and is not a risk you can reasonably impose on the wider public. Many of our high target mature urban trees would be an unacceptable risk.

 

Similarly, I think the lowest value of the Improbable Likelihood of Failure range at 1/1 000 000 would be too high as well. If we take an actuarial perspective and look at some figures that we do know;

 

Number of trees in the UK around 5 000 000 000 (5 billion)

Population of the UK around 62 000 000

Risk of death from tree failure in the UK 1/10 000 000

Nearly all the trees don’t fall down each and every year

 

Then I think setting the lower value of Improbable Likelihood of Failure at 1/1 000 000 is erring on the risk averse ‘safe’ side.

 

When looking for common ground between QTRA and the Risk BMP one of possible problems that popped up is that 3/4 of the Risk BMP’s Likelihood of Failure ranges

 

Imminent = 1/1

Probable = 1/1 - >1/2

And the top value of Possible = <1/2

 

Fall into the highest Probability of Failure (PoF) Range 1 : 1/1-1/10 with QTRA.

 

The Possible Likelihood of Failure range goes from <1/2 down to “but is unlikely” and looks like it covers all seven QTRA PoF ranges if the upper value of ‘Improbable’ is less than <1/1 000 000; which it must surely be.

 

Cheers

 

Acer ventura

Edited May 19, 2014 by Acer ventura

[daltontrees]

To put what the Risk BMP risk rankings are saying in terms of tangible numbers in relation to say schools, which I opened the thread with.

 

If you have a class of 30 children and a year later 14 of them are dead, this would be ranked as a Low risk.

 

If 29 of the 30 died, this would be ranked as a Moderate risk.

 

 

Sorry, I don't follow this. Have 14 children been killed by one tree? Doesn't the risk arise from a hazard and the harm is done when a tree fails and then once failed that hazard cannot fail again?

[daltontrees]

Another thought, would analysis of the ISA system in numerical terms not benefit from a Monte Carlo simulation to better define the overlaps?

[daltontrees]

Another question if I may?

 

Are there equivalents in the USA and Australia of the ToR framework? And if not, do you consider it universal enough to be applicable there?

[arb culture]

Can anyone point out where I’ve gone wrong here?

 

As I said in the opening post, one the reasons I've had my sleeves rolled up and been looking at this in so much detail is because of requests about whether QTRA and the Risk BMP can work in tandem from TRAQ accredited arborists and QTRA Registered Users who want to be ISA accredited to assess tree risk. I’ll post the QTRA outcomes in the Risk Matrix tomorrow.

 

Cheers

 

Acer ventura

 

Yes, I can, but as someone who's not a registered QTRA user, what's in it for me?

 

I don't want to be unhelpful when it's a matter of interest to wide range of arbs, or where questions are of a not for profit nature, but I get the impression that what you are trying to achieve here is solely for the monetary benefit of QTRA Ltd.

 

BTW, and as an aside, has this new Monte Carlo method of tree risk assessment been peer reviewed?

[jomoco]

Yes, I can, but as someone who's not a registered QTRA user, what's in it for me?

 

I don't want to be unhelpful when it's a matter of interest to wide range of arbs, or where questions are of a not for profit nature, but I get the impression that what you are trying to achieve here is solely for the monetary benefit of QTRA Ltd.

 

BTW, and as an aside, has this new Monte Carlo method of tree risk assessment been peer reviewed?

 

Touché mate!

 

The wise discerning eye!

 

Jomoco:001_smile:

[Acer ventura]

 

Your original post makes it pretty clear what you would like to do. But it's still not clear why you want to do it. I mean, you are representing the commercial interests of QTRA Ltd., are you not?

 

Hi Jules

 

I’m not. I’m representing myself. My personal interest and professional development in tree risk assessment and tree risk assessment systems. And because it was raised by people I’d trained and talked to who are ISA TRAQ accredited, or who are interested in becoming so.

 

On the commercial interest side. Just to clarify, I don’t draw a salary from QTRA. I do get paid by QTRA only when I run workshops, which I disclosed in my opening post. I use QTRA because I think it’s the best tree risk assessment methodology, and for that reason I’m happy to train others in its use, help develop it, and discuss its application on forums such as this. I used to use Matheny & Clark's Hazard Rating system in the 1990s until QTRA came along. If tree risk assessment system comes along that’s better than QTRA then I’ll drop it and use that.

 

I sould also explain that I have been working on this issue for about 6 months' date=' covering it as part of a bigger piece of work that at the time you posted last week I was tidying up for submission for peer review and publication.[/quote']

 

I’d be interested to read what you’ve got to say. Any idea of where and when it might be available?

 

One piece of information had been missing' date=' namely a copy of Matheny & Clark's 1994 book, which I got through the post last week. I am glad I waited for it, because the hazard rating it introduced remains the foundation of most if not all proprietary quantitative and qualitative tree risk assessment methods.[/quote']

 

I’m not sure it does. The hazard rating system added ordinal numbers, and the Risk BMP, quite correctly, specifically points out this shouldn’t be done.

 

For those of you who might be unsure about this point:

 

Cardinal numbers tell you how much of something there is like 1 climber, 2 groundsmen, or an unexpected item in the bagging area. You can use them to count and add.

 

Ordinal numbers rank things, or tell their order, like you came last in a dwarf tossing competition, or you’ve won second prize in a beauty contest.

 

Adding or multiplying ordinal numbers can mean very little. For example. Imagine one of the most lip-smacking delicious meals you’ve ever eaten. Give it 5 stars. Now imagine you’ve eaten a meal consisting largely of lukewarm over-boiled brussels sprouts. Give it 1 star. Now, if you ate five of those 1 star brussels sprouts dishes is it the same as eating one 5 star meal.

 

Cheers

 

Acer ventura

[Acer ventura]

Sorry, I don't follow this. Have 14 children been killed by one tree? Doesn't the risk arise from a hazard and the harm is done when a tree fails and then once failed that hazard cannot fail again?

 

Hi Jules

 

I was looking to express what the upper value of a risk ranking of less than <1/2 per annum for a fatality would mean in language outside of probabilities. Another way. Consider there are 30 trees in the school with a Risk BMP ranking of Low risk <1/2 for a fatality per annum. What’s the worst that could happen and the risk ranking still be correct?

 

Does that clarify it?

 

Cheers

 

Acer ventura

[Acer ventura]

Another thought, would analysis of the ISA system in numerical terms not benefit from a Monte Carlo simulation to better define the overlaps?

 

Hi Jules

 

I was going to run the QTRA (Monte Carlo simulation) outputs tomorrow and populate the Risk Matrix as far as I’ve been able to work out.

 

As you might have figured out from my response to Paul, the overlapping Risk BMP Likelihood ranges all fall within one of the QTRA ranges so it’s not an issue with running the QTRA side of things. There are some other problems with compatibility though, which I’ll go through.

 

Cheers

 

Acer ventura