Quantifying risks from many trees

[stevelucocq]

If you are not already a subscibed member of the QTRA forum, ( this is likely the case as a licensed user ) then I would suggest perhaps you could change your preferences to receive mail as it is generated. There are a number of examples that appear in real time aswell as some discussion around related issues of risk assessment and in particular, the way QTRA is used and thought about by those trained in it's use. But then you knew that didnt you?

 

Hi If you check the QTRA discussion group I used it a few days ago. I was interested in this example in thread regarding 1/10,000 with 10,000 trees as I got it completely wrong. I am keen to read about other examples to help me think further about probability.

[arbclimber]

Hi If you check the QTRA discussion group I used it a few days ago. I was interested in this example in thread regarding 1/10,000 with 10,000 trees as I got it completely wrong. I am keen to read about other examples to help me think further about probability.

 

I know next to nothing about QTRA so please feel free to completely ignore my advice but it occurs to me that if it is the probability part of it that is confusing, why not read up generally about probability, it might help. Probability, when you study it, in depth, is fascinating and confusing, in equal measures. Just thinking that some probability based, general study may help.

 

I may well be talking rubbish but hope its helpful.

[Bundle 2]

I know next to nothing about QTRA so please feel free to completely ignore my advice but it occurs to me that if it is the probability part of it that is confusing, why not read up generally about probability, it might help. Probability, when you study it, in depth, is fascinating and confusing, in equal measures. Just thinking that some probability based, general study may help.

 

I may well be talking rubbish but hope its helpful.

 

This is quite good advice Steve , to be fair. It is the aspect most often giving rise to doubts and questions for us newbies to QTRA. I hope I am not telling you anything Mike hasnt or wouldnt i suspect say also. Training is actually only a very limited insight to the system.

PoF will take time to see in a "realistically" proportionate value.

I would add though that perhaps for many arborists,( and I may well be chastised for taking or vocalising this view, it is my own and not handed down from QTRA I hasten to add ) for many there is no need to understand the mathematics in detail or even to some extent, in principle. This is ever more true I think with the upcoming release of software that can be used with handheld PDA's or toughbooks and the like. My own view is that a better understanding of the maths has gotta help but I studied maths to A'level and thought it was fun!

The difficulties can arise when those of us with only a limited grasp of the method try to apply, or miss apply I suppose, theoretically. No amount of reading is gonna sort out fundamental failure to grasp the underlying theory. It may just have the opposite effect. This is a long winded way of saying that Im not convinced that we all need to be mathematicians to use it and reading may infact "undo" the work QTRA put in when training students in it's use. I noticed Mike was quite quick to suppress wrong turns whilst keeping it all as simple as he can. I think the same criticisms and questions come up over and over tbh.

 

If you are looking to read the math, try....

" An introduction to Statistical Methods and Data Analysis" by a Dr Lyman Ott. isbn 0-87872-134-7

Otherwise I am trying to get to reading "Risk" by Dan Gardner and irrationality by Stuart Sutherland. I have no idea what to expect from the last 2 but Ott is heavy dude!

I hope it helps.

[arbclimber]

Maybe I wasn't talking rubbish after all. I understand probability, its trees I dont know much about:laugh1:

[stevelucocq]

Hi thanks for the replies and its all helping me gain a better grasp of QTRA. I have a potential piece of work coming up and I am keen to carry it out under the QTRA methodology. As bundles 2 states I do not want to misapply the methodology and so I am getting myself up to speed.

 

Also I feel ok with estimating targets value and size of the hazard. It giving the value for the potential of failure seems like the tricky bit. High values from 1/1 to 1/100 seems ok to estimated but when you get below that I am struggling to make a estimation. Any help with this and examples would be much appreciated.

 

Also I have been on the QTRA forum since the course last summer but never had to be a power user of it until possibility now. I will have a trawl through the threads.

 

Thanks.

Steve

[Bundle 2]

Also I feel ok with estimating targets value and size of the hazard. It giving the value for the potential of failure seems like the tricky bit.

 

Thanks.

Steve

 

 

Seems to me that you might benefit from making the calculations more than once. By this I mean, as Im sure you will have been shown during the induction training to the use of QTRA, with different inputs. Try mixing it up so to speak. It will be by seeing the way inputs determine the output value that will throw the most valuable insights to the fore. I would also urge you to consider whether the output seems reasonable at the final analysis. If it seems way off, against your gut feeling, then I would suggest it probably is!

Remember, the wheel and initial survey is only an indication of the need to consider the risk in detail, allowing other, perhaps more "pertinent" factors to the fore...I dont know, like management resource pressures , conservation and the like.....Im rambling so Ill shut up!

cheers