On 01/18/2014 04:39 AM, 明 wrote:
Dear all
      I have a model with four paramters, I want to estimate the parameter 
uncertainty, so Bayesian analysis with MCMC method is applied.
      But every sigle mcmc chain seems give quite different parameter marginal 
distributions.
      In order to get the true parameter marginal distributions, I do like this:
      (1) I take 100 MCMC chain, and each chain has 10000 iterations.
      (2) caculate the different parameter marginal distributions according to 
the frequence of paramter in step 1 sampling.
      The result seems reasonable. but is it right?
      Looking forward for your reply, Thanks in advance
Han Ming
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Have you checked for convergence? If the chains are giving different marginal distributions, this suggests they haven't converged, so they are not sampling from the correct posterior distribution (or, at least, some chains aren't).

Bob

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