6: Market Basket Analysis and Text Analysis Flashcards
What does a leverage value of 0 indicate?
A leverage value of 0 indicates independence between A and B.
Between which values does the lift measure range?
From 0 to infinity.
Between which values does leverage measure range?
Between -1 and 1.
What does it mean if the measure lift(A→B) = 3.5?
That a customer who buys item A will be 3.5 times more likely to buy B (at same purchase).
What does it mean if the measure Lift(A→B) > 1?
That the presence of A in this transaction causes a higher probability of B in the same transaction.
What does the lift (A→B) measure compare?
It compares P(B∣A) with P(B), i.e, the probability of B occurrence given A is present and the probability of B occurrence without knowing about A.
Definition of support A & B?
The proportion of times events A and B occurred together is referred to as the support of A and B.
How do we measure co-incidences?
We look for products who have 1s at the same row (transaction) in the incidence matrix.
Definition of confidence?
Confidence measures the percentage of times that item B is purchased, given that item A was purchased. (Confidence of an association rule is a measurement of its predictive power or accuracy).
Formula for confidence of B given A?
Confidence(A→B) = P(B|A) = support (A & B) / support (A) = (count (A & B) / N) / (count (A) / N)
What is the idea of using the lift measure and not only the confidence measure (A→B)?
If B (following itemset = consequent) is a very frequent itemset, confidence related to B will always be high.) Lift is another metric to be considered together with confidence.
Formula for lift of A on B?
Lift(A→B) = P(B|A) / P(B)
What does the leverage of A and B measure?
The strength of association between A and B.
What does the conditional probability of B given A express?
the probability of event B, knowing that event A has occurred.
Which two parts does an association rule consist of?
The antecedent → the consequent.
