Ventana software support forum

1 - right 2 - https://en.wikipedia.org/wiki/Durbin%E2%80%93Watson_statistic 3 - there are other, less complete ways, but nothing built in (this is something we're thinking about) Thanks Tom. I am wondering WHEN a system dynamics model is not affected by autocorrelation. Indeed, according to Barlas ...

1. And, do you mean autocorrelation of the residuals?

2. Thwe payoff reporting provides the Durbin-Watson, but how to interpret it?

3. In case there is autocorrelation, is the Kalman Filter the only option for using MCMC?

However, all of this assumes that your payoff elements are properly weighted (the SD used to determine the weight is really the standard error of the measurements), no autocorrelation (the Kalman Filter takes care of that, if you can use it). And of course, you implicitly assume that the model is r...

The same question in case I use MCMC after the Powell optimisation. If I set: :OPTIMIZER=Off :SENSITIVITY=Payoff_MCMC=1.92 List of parameters Is it always true that I can assess the confidence bounds without making any assumptions that require a well-behaved (e.g., ellipsoid) likelihood surface? And...

Hi, how to evaluate the confidence bounds of the calibrating parameters by using MCMC as a standalone method? Should I set SENSITIVITY=PAYOFF MCMC equal to a certain #value?? For example, I set the distribution of my payoff as Gaussian. If I use MCMC as a standalone method, can I set SENSITIVITY=PAY...

Vensim at vensim.com works. Hi Tom, now it works! I just changed the MCINITMETHOD. If i use the hybrid method, it now works perfectly. I have one question about how to interpret the results: I do, for examples, 20'000 MCMC simulations; then, in the output myrun_MCMC_sample.tab I have all the accept...

I think this is a known bug that will be fixed in the next release. If you can share the model & supporting files (post here or email), that would help us to ensure it's fixed. Also, try turning off the payoff report. Whether 110 is a lot depends on the structure of the problem, but I'd say tha...

If you use MCMC, you avoid the question of determining the proper X^2 cutoff entirely. But then you should use the Gaussian option in order to have the likelihood properly scaled (Normal is the sum of squares, whereas Gaussian uses the sum/2, corresponding with the actual likelihood for the distrib...

2. Correct. Thank you Tom, this will really help to find a proper way to set the weight in the payoff. I have just an observation regarding the chi-square distribution. Since, by definition, the chi-square with k degrees of freedom is the distribution of a sum of the squares of k independent standa...

1 - correct, as long as you're not estimating the weights. If you're estimating the weights, you need to use Distribution=Gaussian (or there are a few others that work). The Gaussian is the same, except that the likelihood includes an extra term for the weight. You can use the log transform, as lon...

Hello! I have a doubt regarding the MCMC option in Vensim DSS. I would like to evaluate the confidence bounds of all the parameters that I calibrated in my model. In the Help ( https://www.vensim.com/documentation/index.html?mcmc_options.htm ), it is written "If the payoff is a properly weight...

Hello! I have a doubt regarding the MCMC option in Vensim DSS. I would like to evaluate the confidence bounds of all the parameters that I calibrated in my model. In the Help ( https://www.vensim.com/documentation/index.html?mcmc_options.htm ), it is written "If the payoff is a properly weighte...

(I think you'll need to remove the NA values, as it won't read text) Thank you Tom. You have been very helpful! I tried to implement both of them. Since for "income" I have just the initial and final data values, I had to increase a lot the weight of "Income" payoff, otherwise i...

Good afternoon everybody, I am writing in order to kindly ask you for a help regarding the calibration with Vensim DSS using "soft" sources of data. In order to be clear, I upload the file that I will use to explain better my question. In the file, you can see a simple Bass model that repr...