The Support and Confidence Given rule x&y=>Z Support,S=P(x∪YuZ) where AU B indicates that a transaction contains both X and y (union of item sets X and Y) of tuples containing both a &b/ total of tuples Confidence, C=P(ZXUY) P(Z XU Y) is a conditional probability that a transaction having iXUY also contains of tuples containing both X&y&z /# of tuples containing X&y
6 Given rule X & Y => Z ◼ Support, S = P(X Y Z) where A B indicates that a transaction contains both X and Y (union of item sets X and Y) [# of tuples containing both A & B / total # of tuples] ◼ Confidence, C = P(Z | X Y ) P(Z | X Y ) is a conditional probability that a transaction having {XY} also contains Z [# of tuples containing both X&Y&Z / # of tuples containing X&Y] The Support and Confidence
The Support and Confidence Customer Customer buys both Let minimum support 50%, and buys diaper minimum confidence 50%. find out the s and c of 1.A→C 2.C→A Customer buys beer Transaction ID Items Bought 2000 A, B C Answer. 1000 A C A→C(50%,666% 4000 A D 5000 B, E, F C→A(50%,100%) 7
7 The Support and Confidence Transaction ID Items Bought 2000 A,B,C 1000 A,C 4000 A,D 5000 B,E,F Let minimum support 50%, and minimum confidence 50%, find out the S and C of : 1. A C 2. C A Customer buys diaper Customer buys both Customer buys beer Answer: A C (50%, 66.6%) C A (50%, 100%)
How Good is a Predictive model? Response curves How does the response rate of a targeted selection compare to a random selection? 100% Optimal Selection Response Targeted Selection Rate Random Selection Most likely to respond Least likely
8 How Good is a Predictive Model? Response curves - How does the response rate of a targeted selection compare to a random selection?
What is A Lift Ratio? (1) ■ Consider the rule: When people buy diapers they also buy beer 50 percent of the time a It states an explicit percentage (50% of the time) Consider this other rule People who purchase a vcr are three times more likely to also purchase a camcorder The rule used the comparative phrase three times more likely
9 What is A Lift Ratio? (1) ◼ Consider the rule: ◼ When people buy diapers they also buy beer 50 percent of the time. ◼ It states an explicit percentage (50% of the time). ◼ Consider this other rule: ◼ People who purchase a VCR are three times more likely to also purchase a camcorder. ◼ The rule used the comparative phrase “three times more likely”?
What is a Lift ratio?(2) a The probability is compared to the baseline likelihood The baseline likelihood is the probability of the event occurring independently E. g, if people normally buy beer 5% of the time then the first rule could have said 10 times more likely.” The ratio in this kind of comparison is called lift a key goal of an association rule mining exercise is to find rules that have the desired lift 10
10 ◼ The probability is compared to the baseline likelihood. ◼ The baseline likelihood is the probability of the event occurring independently. ◼ E.g., if people normally buy beer 5% of the time, then the first rule could have said “10 times more likely.” ◼ The ratio in this kind of comparison is called lift. ◼ A key goal of an association rule mining exercise is to find rules that have the desired lift. What is A Lift Ratio? (2)