QTRA... V.T.A..... Or Lantra Pro tree inspection

[Amelanchier]

So you can understand why no-one has offered to answer the 1/10,000 question! But it will be somewhere between 1:1 and 1:1.53.

[Amelanchier]

but how many poeple walk there on a gusty day? on a wet and windy day?

 

one day is different to the next in all terms, number of walkers etc etc etc.

 

I think this is a nightmare calculator scenario, but i am listening, but i will take some convincing that statistics are valid

 

One of the golden rules of stats is junk in = junk out. QTRA doesn't try to get it spot on - just as accurate as is 'reasonable' for the given circumstances. Remember we're trying to determine the neccessity of works with a systematic approach. We're not trying to be spot on to 5 decimal places. Provided the working is shown, its just an extension of a professional judgement.

[Amelanchier]

Tony - are you are QTRA licensed user?

 

Fraid so (last time I checked - it might have expired!). I don't get as much use out of as I would like though.

[combined tree services]

personally i think that it is more imprtant to have a wider range of assessment and inspection methods that are able to use , such as QTRA, VTA, etc etc. im sure there are many trees in which QTRA is not appropriate to be used on . please correct me if im wrong but is QTRA not seen as the approved method of calculating the risk factors of trees with both the HSE and AA ?? only asking as im not totally sure

[arb culture]

Thanks Tony

 

Using a calculator your sum with the ten trees can be worked like this :

 

change 9/10 into 0.9 (it's the same thing)

 

Then, rather than 0.9 x 0.9 ...etc

 

type in 0.9 then the xy button then 10 then =

 

For the 1:10,000 question you use 0.9999 rather than 9,999:10,000 to work out the probability of a tree not falling over.

 

Then type in 0.9999 xy button 10,000 = 0.368

 

1-0.368=0.682

= 1:1.582

 

[arb culture]

Now, what is the threshold at which the risk from a tree is deemed unacceptable?

[Bundle 2]

Mmmmm...thats just it,,,0.9 is not the same thing as 9/10. We are talking about probability remember!

"im sure there are many trees in which QTRA is not appropriate to be used on "

i dont know about that mate. It can certainly be used in all situations but it will only ever give you a quantified assessment (ie a probabalistic calculation) If you want a health report or a VTA based appraisal of the mechanics of a trees structure, then you are using the wrong tool! Simple!

[Amelanchier]

Thanks Tony

 

Using a calculator your sum with the ten trees can be worked like this :

 

change 9/10 into 0.9 (it's the same thing)

 

Then, rather than 0.9 x 0.9 ...etc

 

type in 0.9 then the xy button then 10 then =

 

For the 1:10,000 question you use 0.9999 rather than 9,999:10,000 to work out the probability of a tree not falling over.

 

Then type in 0.9999 xy button 10,000 = 0.368

 

1-0.368=0.682

= 1:1.582

 

 

Ha indeed! Fair bit easier... I get a little fuzzy with the scientific notation on my calc, 3.1e06 and all that. I was out with the prediction then? 1:1.53 is more likely than 1:1.58?!?

 

The only problem I ever really had with the QTRA system was referring to the probabilities in the 1/10, 1/100 format - I'd always dealt with probabilities in decimal.

[arb culture]

Bundle, no disrespect, but if you follow the link below to the relevent GCSE bitesize page, I think you will find that 0.9 is the same 9/10.

 

BBC - GCSE Bitesize: Fractions and decimals

 

Unless I've missed something

 

[Amelanchier]

Now, what is the threshold at which the risk from a tree is deemed unacceptable?

 

Aaahh, a true can of worms. Acceptable to whom?