Skip to main content
Interactive 3D/Prior to Posterior
Prior Beta(α, β)
α (prior heads)2.0
β (prior tails)2.0
Observations
Flips: 0 | Heads: 0 | Tails: 0
Posterior Beta(α+k, β+n−k)
Prior mean 0.500
Posterior mean 0.500
Posterior mode 0.500
95% CI [0.094, 0.906]
Conjugate prior.
Beta is conjugate to Binomial: the posterior is another Beta. More data = narrower distribution = more certainty about θ.

Prior to Posterior - Interactive Visualization

Bayesian inference updates beliefs as data arrives: posterior ∝ likelihood × prior. The Beta-Binomial model is the canonical example: Beta prior + Binomial likelihood = Beta posterior. Start with a prior belief about coin fairness (α, β), then observe coin flips. Each flip updates the posterior - more data swamps the prior. This is the essence of Bayesian learning.

  • Set prior beliefs with α and β sliders for the Beta distribution
  • Click Flip Coin to observe one flip and update posterior live
  • Watch posterior narrow as more flips are observed (uncertainty reduces)
  • See that strong priors (large α, β) require more data to be overcome
  • Foundation for Bayesian neural networks, Thompson sampling, and A/B testing

Part of the EngineersOfAI Interactive 3D - free interactive visualizations covering every major concept in machine learning and AI engineering. Hover any element for a plain-English explanation. No code required.