Re:How (not) to forecast an election: Analysis via a hierarc...
by froogle on Sunday November 27, 2016 @07:19PM
(#13052513)
PredictWise is not a prediction market. It's an aggregate of them, with David Rothschild's own personal special sauce added on top - which, in this case, is why it was "wrong".
PredictWise's mistake was that it assumed polling errors would not be correlated[1]. (He actually had a fight with Nate Silver over this.)
Nate Silver had, in advance, stated that polling errors would be correlated[2] (rightfully, as it turned out), which is part of why 538's model turned out to be closer to reality than PredictWise's.
The actual betting markets, which PredictWise was pulling data from, were in the range of 20-30% Trump. Much more bullish.
PredictWise's mistake was that it assumed polling errors would not be correlated[1]. (He actually had a fight with Nate Silver over this.)
Nate Silver had, in advance, stated that polling errors would be correlated[2] (rightfully, as it turned out), which is part of why 538's model turned out to be closer to reality than PredictWise's.
The actual betting markets, which PredictWise was pulling data from, were in the range of 20-30% Trump. Much more bullish.
[1] http://predictwise.com/blog/2016/09/poll-aggregation-fight/
[2] http://fivethirtyeight.com/features/election-update-why-our-...