Meaning of Bias and Variance?

Bias: how unfair is something towards other

Variance: how likely something changes with respect to others

Thing to remember?

High Bias: under fitting

High Variance: over fitting

What is High Bias and High Variance?

Assume there are two examiners determining weather forecast.

Where it rains only when it is humid and does not when it is hot, windy or freezing.

You ask Examiner A (Despite of his training, he is too favored towards rain because he loves rain) and Examiner B (a bookworm who completely remembers the training he had):

 Questions (Conditions) Examiner A Examiner B Sir, it’s extremely hot today, will it rain? Yes No Sir, its little windy out here, will it rain? No No Sir, its freezing will it rain? Yes No Sir, it’s humid out here, will it rain No Yes

During the test, Examiner A is unable to predict most of them correctly as he is biased towards rainfall. This condition is called under fitting.

Examiner B successfully predicted whether it will rain or not. But being a book worm, he is unknown to the conditions not described in the book during training.