Tree risk lessons | The straw Poll fallacy

2021-04-26 8:23 AM | Admin (Administrator)

In the previous post we looked at VALID's Goldilocks Likelihood of Occupancy canvas to explore categories that are not too wide, and not too narrow, that are just right.

This Likelihood of Occupancy canvas is useful to examine tree risk decision-making at the High Court in the UK’s landmark Poll v Bartholomew Judgment.

Poll v Bartholomew - VALID Likelihood of Occupancy

In Poll, a motorcyclist was seriously injured by a falling Ash stem. The Judge found for the Claimant because the tree was ‘High Risk.’

In their reports, the Claimant’s expert said the tree was ‘High Risk’ and the Defendant’s expert didn’t mention any risk. Yet in their Joint Statement, the experts agreed the tree was a ‘Medium Risk.’

Naturally, the expert’s opinions left the court scratching its head and it had to ask them to produce a Second Joint Statement to define what they meant by high and medium risk.

In the Second Joint Statement, the experts told the court the tree was ‘High Risk’. However, they concluded the risk was high after they'd assessed the Likelihood of Occupancy for a minor road at 50%, when in fact it was 1%. The experts overvalued the occupancy by a whopping factor of 50. This gaffe was so enormous the tree was in fact a ‘Medium Risk’ and not a ‘High Risk.’

The Judge would’ve found for the Defendant if the tree was a ‘Medium Risk.’

Poll v Bartholomew | Expert Evidence - Likelihood of Occupancy