CS228 Weekly Quiz

CS228: Probabilistic Methods in AI
Winter 2008
Weekly Quiz

[ Detailed Question/Answer Statistics ] [ Score Frequency Table ]

Note: Statistical results may be approximate, and may be rounded up (or down, as the case may be) to the nearest whole number. In Detailed Question/Answer Statistics, percentages which do not add up to 100% may be due to students skipping questions, questions which were added or modified after a quiz or test was already in progress, or answers/distractors which were added or modified after a quiz was already in progress. The Question/Answer statistics reflect the current state of a particular quiz, and thus may not be exact for quizzes which have been modified after someone has taken them.

Students taking the quiz: 66 Total quizzes taken: 66

Overall Score Statistics:
Mean	Median	Mode	Lowest	Highest
89.55%	90%	100% (29)	30%	100%

Score Frequency Table

Frequency of Scores
Score	Number of Students
100%	29
90%	21
80%	9
70%	4
50%	1
40%	1
30%	1

Detailed Question/Answer Statistics:

Question 1: Which of the following is a context-specific independence that does NOT exist in the tree CPD below. Answers: 1. a) 2. b) 3. c) 4. d) 5. All context-specific independencies are correct.
Type	Answer	Responses	Percent
Correct:	d)	64	97%
Distractor:	a)	0	0%
Distractor:	b)	0	0%
Distractor:	c)	1	2%
Distractor:	All context-specific independencies are correct.	1	2%
Question 2: In the Tree CPD below, which of the following is equal to .6? (The first value in the parentheses corresponds to D=0 and the second value corresponds to D=1.) Answers: 1. P(B=1 \| A=1) 2. P(C=0 \| A=1, B=0) 3. P(D=0 \| A=1, B=1) 4. P(D=0 \| A=1, B=0, C=0)
Type	Answer	Responses	Percent
Correct:	P(D=0 \| A=1, B=1)	62	94%
Distractor:	P(B=1 &KPHHASH124; A=1)	0	0%
Distractor:	P(C=0 &KPHHASH124; A=1, B=0)	2	3%
Distractor:	P(D=0 &KPHHASH124; A=1, B=0, C=0)	2	3%
Question 3: In the following Bayesian network, the node B is a deterministic function of its parent A. Which of the following is an independence statement that holds in the network? Answers: 1. A B \| C,D 2. C D \| A 3. A D \| C 4. B C \| D
Type	Answer	Responses	Percent
Correct:	C <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> D \| A	63	95%
Distractor:	A <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> B &KPHHASH124; C,D	1	2%
Distractor:	A <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> D &KPHHASH124; C	0	0%
Distractor:	B <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> C &KPHHASH124; D	2	3%
Question 4: Which set of variables represent the Markov blanket of the variable X in the network shown below? Answers: 1. A,B,C, and D 2. B, C, and F 3. B, C, F, and E 4. B and C
Type	Answer	Responses	Percent
Correct:	B, C, F, and E	62	94%
Distractor:	A,B,C, and D	0	0%
Distractor:	B, C, and F	2	3%
Distractor:	B and C	2	3%
Question 5: Which of the following Bayesian Networks does not have a corresponding Markov Network that encodes precisely the same set of independence assumptions? (That is, for which network does there not exist a Markov Network that is a perfect map of that Bayesian Network?) Answers: 1. A) 2. B) 3. C)
Type	Answer	Responses	Percent
Correct:	B)	62	94%
Distractor:	A)	1	2%
Distractor:	C)	1	2%
Question 6: Which of the following Markov networks does not have a corresponding Bayesian Network that encodes precisely the same set of independence assumptions? Answers: 1. A) 2. B) 3. C)
Type	Answer	Responses	Percent
Correct:	B)	63	95%
Distractor:	A)	0	0%
Distractor:	C)	2	3%
Question 7: How many undirected edges does the moralized graph of the following Bayesian network contain? Answers: 1. 3 2. 4 3. 5 4. 6 5. 7
Type	Answer	Responses	Percent
Correct:	6	56	85%
Distractor:	3	1	2%
Distractor:	4	0	0%
Distractor:	5	8	12%
Distractor:	7	0	0%
Question 8: Which of the following is a valid grounded model for the plate shown? Answers: 1. (a) 2. (b) 3. (c)
Type	Answer	Responses	Percent
Correct:	(c)	57	86%
Distractor:	(a)	7	11%
Distractor:	(b)	0	0%
Question 9: Which of the time-series graphs satisfies the Markov assumption? Answers: 1. (a) 2. (b) 3. (c) 4. None of the above
Type	Answer	Responses	Percent
Correct:	(b)	39	59%
Distractor:	(a)	3	5%
Distractor:	(c)	12	18%
Distractor:	None of the above	11	17%
Question 10: In the following DBN, which independence assumption is FALSE. Answers: 1. X^(t-1) X^(t+1) \| X^(t) 2. O^(t) X^(t-1), X^(t+1) \| X^(t) 3. O^(t) O^(t-1) \| X^(t) 4. O^(t) O^(t-1)
Type	Answer	Responses	Percent
Correct:	O<sup>(t)</sup> <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> O<sup>(t-1)</sup>	63	95%
Distractor:	X<sup>(t-1)</sup> <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> X<sup>(t+1)</sup> &KPHHASH124; X<sup>(t)</sup>	0	0%
Distractor:	O<sup>(t)</sup> <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> X<sup>(t-1)</sup>, X<sup>(t+1)</sup> &KPHHASH124; X<sup>(t)</sup>	2	3%
Distractor:	O<sup>(t)</sup> <img src="http://www.stanford.edu/class/cs228/Images/perp.gif"/> O<sup>(t-1)</sup> &KPHHASH124; X<sup>(t)</sup>	0	0%