Who has not heard that Bayesian statistics are difficult, computationally slow, cannot scale-up to big data, the results are subjective; and we don't need it at all? Do we really need to learn a lot of math and a lot of classical statistics first before approaching Bayesian techniques. Why do the most popular books about Bayesian statistics have over 500 pages? Bayesian nightmare is real or myth? Someone once compared Bayesian approach to the kitchen of a Michelin star chef with high-quality chef knife, a stockpot and an expensive sautee pan; while Frequentism is like your ordinary kitchen, with banana slicers and pasta pots. People talk about Bayesianism and Frequentism as if they were two different religions. Does Bayes really put more burden on the data scientist to use her brain at the outset because Bayesianism is a religion for the brightest of the brightest?

Since their early days, humans have had an important, often antagonistic relationship with uncertainty; we try to kill it everywhere we find it. Without an explanation for many natural phenomena, humans invented gods to explain them, and without certainty of the future, they consulted oracles. It was precisely the oracle's role to reduce uncertainty for their fellow humans, predicting their future and giving counsel according to their gods' will, and even though their accuracy left much to be desired, they were believed, for any measure of certainty is better than none. As society grew sophisticated, oracles were (not completely) displaced by empiric thought, which proved much more successful at prediction and counsel. Empiricism itself evolved into the collection of techniques we call the scientific method, which has proven to be much more effective at reducing uncertainty, and is modern society's most trustworthy way of producing predictions.

In this article, I will provide a basic introduction to Bayesian learning and explore topics such as frequentist statistics, the drawbacks of the frequentist method, Bayes's theorem (introduced with an example), and the differences between the frequentist and Bayesian methods using the coin flip experiment as the example. To begin, let's try to answer this question: what is the frequentist method? When we flip a coin, there are two possible outcomes -- heads or tails. Of course, there is a third rare possibility where the coin balances on its edge without falling onto either side, which we assume is not a possible outcome of the coin flip for our discussion. We conduct a series of coin flips and record our observations i.e. the number of the heads (or tails) observed for a certain number of coin flips. In this experiment, we are trying to determine the fairness of the coin, using the number of heads (or tails) that we observe.

Frequentist Statistics tests whether an event (hypothesis) occurs or not. It calculates the probability of an event in the long run of the experiment. A very common flaw found in frequentist approach i.e. dependence of the result of an experiment on the number of times the experiment is repeated. Bayesian statistics is a mathematical procedure that applies probabilities to statistical problems. It provides people the tools to update their beliefs in the evidence of new data.

I did a webcast earlier today about Bayesian statistics. Some time in the next week, the video should be available from O'Reilly. In the meantime, you can see my slides here: And here's a transcript of what I said: Thanks everyone for joining me for this webcast. At the bottom of this slide you can see the URL for my slides, so you can follow along at home. I'm Allen Downey and I'm a professor at Olin College, which is a new engineering college right outside Boston. Our mission is to fix engineering education, and one of the ways I'm working on that is by teaching Bayesian statistics. Bayesian methods have been the victim of a 200 year smear campaign. If you are interested in the history and the people involved, I recommend this book, The Theory That Would Not Die.