Classifier. In a machine learning classification procedure the items are classif
ID: 3306454 • Letter: C
Question
Classifier. In a machine learning classification procedure the items are classified as 1 or 0. Based on a training sample of size 120 in which there are 65 1's and 55 0's, the classifier predicts 70 1's and 50 0's. Out of 70 items predicted by the classifier as 1, 52 are correctly classified. (a) What are the sensitivity and specificity of the classifier? (b) From the population of items where the proportion of 0-labels is 99% (and 1-labels 1%), an item is selected at random. What is the probability that the item is of label 1, if the classifier says it is.Explanation / Answer
a) sensitivity = correctly classified/total 1's =52/65=4/5 =0.8 ~80%
specifiicity = correctly identiified 0;s /total 0's =(50-(65-52))/55 =37/55=0.6727 ~ 67.27%
b)probabilitythat classifier says item is 1=P(item is 1 and classifer says it is 1+item is not 1 and classifier says it is 1)
=0.01*0.8+0.99*(1-0.6727)=0.3320
heefore probability that item is of label 1; given classifier says so =P(item is 1 and classifer says it is 1)/P( item is 1)
==0.01*0.8/=0.3320 =0.0241