# Bayes Classification

In theory we would always like to predict qualitative responses using the Bayes classifier. But for real data, we do not know the conditional distribution of Y given X, and so computing the Bayes classifier is impossible. Therefore, the Bayes classifier serves as an unattainable gold standard against which to compare other methods.

• In a real life situation why we are not able to calculate the Bayes Classifier ?
• Why can't we calculate the conditional distribution of Y given X ?
• Can some one explanation with an example?

Any help is appreciated.

• It seems as if you have cited the first part from "An Introduction to Statistical Learning: with Applications". Please mark it as a citation (prefix it with >) and add the reference. – Martin Thoma Jan 26 '16 at 18:33