I believe it is silly to even try to assign a numerical probability to any event unless you can rigorously derive that number from antecedent circumstances or events (for instance, it can make sense if you are talking about scenarios involving the results of dice rolls). Thus I find the questions in LW’s annual survey which demand such numbers annoying and pointless.
As for the errors in predictions of the time or money it will take to build some promised project, there’s no mystery; the individuals making those predictions stand to gain substantial money or prestige if the predictions are believed, so they lie (or at least make the rosiest predictions they expect to get away with making). This especially goes for politicians, who have all the more incentive to lie because the law gives them absolute immunity (from, for example, being sued for fraud) for anything they say during legislative debate.
The way to get reliable data about these things is to create incentives that make it in someone’s best interest to gather and share that reliable data. For most projects, the simplest and easiest way to do this is to have those who want the project built commission it using their own money, rather than do it through the political system.
I believe it is silly to even try to assign a numerical probability to any event unless you can rigorously derive that number from antecedent circumstances or events (for instance, it can make sense if you are talking about scenarios involving the results of dice rolls). Thus I find the questions in LW’s annual survey which demand such numbers annoying and pointless.
As for the errors in predictions of the time or money it will take to build some promised project, there’s no mystery; the individuals making those predictions stand to gain substantial money or prestige if the predictions are believed, so they lie (or at least make the rosiest predictions they expect to get away with making). This especially goes for politicians, who have all the more incentive to lie because the law gives them absolute immunity (from, for example, being sued for fraud) for anything they say during legislative debate.
The way to get reliable data about these things is to create incentives that make it in someone’s best interest to gather and share that reliable data. For most projects, the simplest and easiest way to do this is to have those who want the project built commission it using their own money, rather than do it through the political system.