Bayesian statistics is a system for describing epistemological uncertainty using the mathematical language of probability. In the 'Bayesian paradigm,' degrees of belief in states of nature are specified; these are non-negative, and the total belief in all states of nature is fixed to be one. Bayesian inference is a method of statistical inference in which Bayes' theorem is used to update the probability for a hypothesis as more evidence or information becomes available. Bayesian inference is an important technique in statistics, and especially in mathematical statistics. Bayesian inference is a different perspective from Classical Statistics (Frequenters). For a Bayesian, probability is more epistemological. Posterior probability (in lay terms) is the updated belief on the probability of an event happening given the prior and the data observed.