[R] ?OT: Probabilistic Simulation

Polwart Calum (County Durham and Darlington NHS Foundation Trust) calum.polwart at nhs.net
Sat Dec 19 00:16:51 CET 2009


Sorry this may well be defined as Off Topic.  I apologize in advance.

I am interested in performing what I think would be a probabilistic sensitivity simulation.  I've done some crude ones before in excel but I'm wondering if R can help me do it more effectively?

I have a set of theoretical variables for simplicity lets use (what I think) is an easier example:  I have a peg and a hole which I want to predict how often they would not fit together securely.

The peg should be 1.8mm in diameter.
But there are some variables which might affect if it is actually 1.8mm but I'd expect it to be normally distributed around 1.8mm with a known standard deviation.  There are also variables such as temperature which would influence if the peg was the correct size (there would be a known relationship to temperature, and a mean temperature with a standard deviation would be known)

The hole should be 1.8mm diameter as well.  Again there are variables that affect if it is, drill size, drilling method, substrate being drilled, temperature at time of drilling, temperature at time of fitting peg (would be same as above).  I'd be looking to model if the peg would fit in the hole, AND if it fitted how well it fitted.

I'd then want to run a simulation of say 500 scenarios, randomly picking temperature, hole characteristics etc for each simulation.    From there I'd get the number of times in 500 samples the peg wouldn't fit.  I could then try adjusting a variable - say using a different drilling method and see if that 'easier' but less reliable drilling method actually would affect the number of times the peg didn't fit the hole properly.

So from what I understand this is a MonteCarlo simulation of probability.  And this is where I go off topic!  Am I right?  I know its off topic - so what I'd like to know is can someone point me to where I can find out?

Then if it is a monte-carlo can someone point me to a good description of how to get R to model this?

Ta

Calum

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