Homework 4

Answer the following questions: (10 point each)

1. Consider the data set shown in Table below:

(a) Estimate the conditional probabilities for

P (A|+), P (B|+), P (C|+), P (A|-), P (B|-), P (C|-)

(b) Use the estimate of conditional probabilities given in the previous question to predict the class label for a test sample (A=0, B=1, C=0) using the naive Bayes approach.

(c) Estimate the conditional probabilities using the m-estimate approach, with p: I/2 and m:4.

(d) Repeat part (b) using the conditional probabilities given in part (c).

(e) Compare the two methods for estimating probabilities. Which method is better and why?

2. Consider the data set shown in Table below:

(a) Estimate the conditional probabilities for

P (A = 1|+), P (B = 1|+), P (C = 1|+), P (A = 1|-), P (B = 1|-), P (C = 1|-)

using the same approach as in the previous problem.

(b) Use the conditional probabilities in part (a) to predict the class label for a test sample (A =1, B=1, C=) using the naive Bayes approach.

(c) Compare P (A=1), P (B=1), and P (A=1, 8=1) State the relationships between A and B.

(d) Repeat the analysis in part (c) using P (A=1), P (B=0), and P(A=1, B=0).

(e) Compare P (A=1, B=1|Class=+) against P(A=1|Class=+) and P (B=1|Class = +). Are the variables conditionally independent given the class?

3. For each of the Boolean functions given below, state whether the problem is linearly separable.

(a) A AND B AND C

(b) NOT A AND B

(c) (A OR B) AND (A OR C)

(d) (A XOR B) AND (A OR B)

4. Following is a data set that contains two attributes, X and Y, and two class labels, “+” and “-“. Each attribute can take three different values: 0, 1, or 2. The concept for the “+” class is Y = 1 and the concept for the “-” class is X = 0 V X = 2

(a) Build a decision tree on the data set. Does the tree capture “+” and the “-” concepts?

(b) What are the accuracy, precision, recall, and F1-measure of the decision tree? (Note that precision, recall, and F1-measure are defined with respect

to the “+” class.)

(c) Build a new decision tree with the following cost function:

= 0, if i = j;

C (i, j) = 1, if i = +, j = -;

= Number of – instance, if i = -, j = +;

Number of – instance

(Hint: only the leaves of the old decision tree need to be changed.) Does

the decision tree captures the “+” concept?

(d) What are the accuracy, precision, recall, and F1-measure of the new decision tree?

5. Given the Bayesian network shown in Figure below, compute the following probabilities:

(a) P (B = good, F = empty, G = empty, S = yes).

(b) P (B = bad, F = empty, G = not empty, S = no).

(c) Given that the battery is bad, compute the probability that the car will start.

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