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What is Gibbs sampling?

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Answer

  • Special MCMC: sample each parameter (or block) from its full conditional p(θj    θj,  D)p({\theta}_{j}\; \mid \;{\theta}_{- j}, \;D), one at a time.
  • Guaranteed acceptance (α = 1) when full conditionals are known.
  • Works well for conjugate hierarchical models, Bayesian networks, LDA.
  • Weak in strongly correlated posteriors — slow mixing.
  • Modern alternatives (HMC, NUTS) are usually better default, but Gibbs is still standard when conjugacy makes full conditionals trivial.
Check yourself — multiple choice
  • Same as HMC
  • Sample each parameter from its full conditional p(θj    θj,  D)p({\theta}_{j}\; \mid \;{\theta}_{- j}, \;D); no rejection; great for conjugate / LDA / Bayes nets; slow in correlated posteriors
  • Random
  • Not MCMC

Gibbs: draw from full conditionals; α=1; slow when correlated.

#bayesian#mcmc

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