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I am just discovering Association Rules, but am a little confused, particularly with the interpretation of the results. My main question is - is the Lift for two items always the same in both directions? Meaning does Lift(B → A) always equal Lift(A → B)?

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The answer to your question would be straightforward from looking at the formula.

$$ \operatorname{lift}(X \to Y) = \frac{\operatorname{P}(X \cap Y)}{\operatorname{P}(X)\operatorname{P}(Y)} $$

The expression is symmetric with respect to $X$ and $Y$.

It is the exponentiation of the pointwise mutual information: a value of 1 indicates no more association than chance.

More information is available from Michael Hahsler, who maintains the arules package.

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