Topic 15

Question 1

Probability That a Test Item x0 Belongs to Class j

Answer 1

Can be estimated from the known class assignments of the training items that are closest to x0 in the feature space.
For a positive integer K and a test item x0:
Find N0, the set of K training items that are nearest to x0.

Question 2

Probability K Nearest Neighbour Equation

Answer 2

Pr(class=j | feature = x0) = 1/K Σi∈N0 I(yi = class j) where I = indicator function, true / false = 1 / 0, K usually chosen to be odd. More simply, just the proportion of neighbours that are the given class