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JGWeissman comments on Bayesian exercise - Less Wrong Discussion

5 Post author: RolfAndreassen 21 September 2011 09:34PM

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Comment author: JGWeissman 21 September 2011 09:56:34PM 18 points [-]

Your problem is that you are effectively assigning probability 1 to the proposition that 1% of launches will fail. Instead, you should have a probability distribution over the fraction of launches that fail. When you observe a launch or a failure, update that probability distribution using Bayes' law, resulting in higher probabilities for lower frequencies after a success.

Comment author: Normal_Anomaly 22 September 2011 01:50:33AM 2 points [-]

It occurs to me that I don't really know how to mathematically handle a probability distribution. How much calculus, if any, is required for this?

Comment author: jsalvatier 22 September 2011 02:53:32PM *  5 points [-]

You need calculus if you're going to try to estimate any continuous quantities, but you can often avoid this by making the variable discrete. Instead of saying "the proportion is a number [0,1]" you say "the proportion is either 0, .25, .5, .75 or 1". This approximates the continuous version and can be done without any calculus.

Comment author: [deleted] 22 September 2011 02:15:44AM *  3 points [-]

To fully interpret a probability distribution you need to use integrals. For example, if I have a probability distribution over the number of heads in 50 coinflips and I want to know the probability that the observed value is going to fall within a certain interval, I have to take the integral of that part of the distribution. You can definitely understand what a probability distribution is without calculus, but you're going to have a hard time actually doing the math.

Edit: It occurs to me that statistical software could do most of the number-crunching for you, which would definitely make things easier.

Comment author: Cyan 22 September 2011 02:56:33AM 2 points [-]

For probability distributions on continuous quantities (such as the proportion of launches that fail), you need to know how to do derivatives and integrals.