Joe Hildebrand: fact arsonist

So, "I'm just trying to be reasonable" professional opinion sprouter Joe Hildebrand put out a tweet saying this:

The problems start with item 1.

Arson definition:  Arson is the act of intentionally and maliciously destroying or damaging property through the use of fire.  Definition from the Australian Institute of Criminology, which is where Joe cites support for his claim.

The AIC report he is presumably relying on is this one, from 2008, which analysed figures from all Australian States, and came up with this conclusion:

Hence, I would have thought that anyone sensible would not claim anything more than "up to half of all bushfires might be deliberately lit", but even that would be misleading.

The correct summary would be "one study indicates that at least 13% of bushfires are deliberately lit, but if all suspicious fires are assumed to also be arson, then it might be as high as 50%".

And even then, it would be fudging somewhat on the qualifications the AIC gave:

Some caution should be taken when considering these figures. Just over 40 percent of vegetation fires across Australia do not have a cause assigned by the responding fire agency. Furthermore, inconsistencies exist between and within agencies in recording data. For example, different agencies may have different thresholds as to when they consider a fire to be deliberate, suspicious or unknown.

Well, that indicates that the exact figure for "arson" is extremely uncertain - and if you want to say that maybe some of the 40% of fires that don't have a cause assigned might be arson, then I would ask "do those fires matter much?  Is a cause not assigned because they were too small to worry about?"   And even if a fire is deliberately lit, it's not always by people who could be held responsible for their action.  Just this week, there was the report of an elderly man believed to suffer from dementia facing 4 charges of lighting fires.   His example might technically be arson, but it's irrelevant to the question of why this fire season is so bad. 

What Hildebrand, if he were honest, or smart, cannot claim is that the study he cites proves that "bushfires are started more by arson than any other cause". [I see in his Twitter defence against lots of people who are pointing this out to him that he now says "I didn't say it caused most fires", as a way of denying that he grouped "suspicious" with "deliberate".   But he must have to some extent to make his claim - "accidental" accounts for 35%, so for "arson" to get above that he has to have arbitrarily added at least 23% to "deliberate" from the "suspicious" column.] 

Why is he surprised that his so-called attempt at common sense consensus fails at step one?

It is, in fact, one of those exercises of "both side-ism" that carries a bias towards one side by giving it a credibility it does not warrant, assisted by his own dodgy number fiddling.