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Inconsistent Results in Firecalc 3.0 - Different Results/Exactly same data
Old 05-24-2009, 03:23 PM   #1
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Inconsistent Results in Firecalc 3.0 - Different Results/Exactly same data

I enter my data into 5 of the panels of FC 3.0. I then "submit" and get the results and chart showing in a 2nd browser tab. It shows a success rate of 65%.

I then go back to the first tab and "submit" again (no changes at all to the parameters). It then gives me 42%. Similarly I get different results EVERY SINGLE TIME that I submit again - 75%, 22% etc etc.

Seems wildly inaccurate. Has anyone seen this type of error?

I am using IE 8.
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Old 05-24-2009, 03:48 PM   #2
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I don't know about the programming, but it seems to me that a Monte Carlo simulation of a scenario that, whatever way you look at it, is likely to have a low probability of success, might indeed show such variation on successive iterations.

Are there any math whizzes around, or programmers? Dory?
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Old 05-24-2009, 03:58 PM   #3
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I entered my numbers and had exactly the same results each time I hit the submit button. We've had no reports of anything like what you are experiencing.

FIRECalc has so many different variables and options it might be beneficial to do a little experiment: Input your information on the first tab only, then hit submit. Hit submit again to be sure you get a consistent end result. Do the same exercise, each time adding another tab, until you find where the error occurs.

With that information someone may be able to help you find the root cause of the error.
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Old 05-24-2009, 04:24 PM   #4
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Quote:
Originally Posted by Meadbh View Post
I don't know about the programming, but it seems to me that a Monte Carlo simulation of a scenario that, whatever way you look at it, is likely to have a low probability of success, might indeed show such variation on successive iterations.

Are there any math whizzes around, or programmers? Dory?
Statistics geek with a computer science degree here.

Monte Carlo simulations don't give the exact same result with each run, but as you increase the number of iterations in each run the "variance" between successive runs should, on average, approach zero. Running 10 iterations will generate a lot of variance, running 20 somewhat less, running 50 less still, and so on until the variance is rather tiny.

Once you reach a large enough number of iterations in a single run, additional iterations do very little to reduce the "delta" from one run to the next, and when that "delta" is small enough for statistical purposes, you don't need to run any more.

So if there are sufficient iterations being done in one run, you should have very little variance from one run to the next. You shouldn't be seeing wildly varying results from one run to the next unless for some reason it's using a different set of input variables each time.
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Old 05-24-2009, 04:33 PM   #5
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Thanks for all the replies. I will try again without selecting the "Random" investment result parameter which is giving me massively different results with each run. I get similar problems using IE8 and Firefox - also using FC 2.0 as well as 3.0.
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Old 05-24-2009, 04:42 PM   #6
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Congratulations, you discovered the source of your inconsistent outcome.

Using the Monte Carlo (random performance) option on tab 5 rather than the FIRECalc default of historical returns will provide (big surprise) random results.
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