As we all wonder how things will look Tuesday evening and Wednesday morning, and then for the next four years, it is interesting to consider how we handle uncertainty in forecasting and modeling.
A range of outcomes on Sunday morning - via 538
|"Mapping uncertainty" - via twitter|
One person, formerly involved with fivethirtyeight, writes that the modeling should be understood as "mapping uncertainty rather than making predictions."
In a response on Our Salem on population forecasting, EconNW said:
Whenever I develop a forecast for a city, I tell them that, while we are required to have a point forecast for 20 years, I know the forecast is almost certainly wrong.
Strong Towns devoted a post to a closely related matter, "A Reminder for Planners: 'Every Projection is Wrong'"
|False precision in the Costco case|
(Final written argument on Remand)
So a perennial question here is, why does our traffic forecasting erase uncertainty and give the false precision of one number for 2035 or 2040 traffic or other future date?
In so many other exercises in forecasting and modeling, those who issue the forecasts and analyze them highlight levels of uncertainty.
Some of the times highlighting a level of uncertainty would make no difference.
|Consultant response to wildly exaggerated|
worries about traffic (Council last week)
An error of several hundred percent here - a 500% error would be 42 trips instead of 7 - at the proposed housing in the German Baptist Church is not at all meaningful for a collector street.
Other times uncertainty has real implications for policy choices.
A forecasting error, well within margins of error, on the State Street corridor might keep us from appropriately adjusting it in a 4/3 safety conversion.
|On State Street:|
An 80th percentile confidence interval should be
about -20% to +10%.
A 95th percentile interval is much wider.
We should insist on an acknowledgement of margin of error and uncertainty on our traffic forecasting, especially when the City and other bodies are making large policy and budgeting decisions on our roads.
(And this note is not about the candidates in the Election; comments about that or them will almost certainly be deleted.)