How to interpret lift in Association rules?

[soliverc]

Not a bug report, just a question. I have googled this and couldn't find an answer.

Let's say I am interested in the item "eggs" alone, and I have 300+ itemsets associated with "eggs". Each of these item sets have a lift of 1.5, 1.6 etc. etc. and lift(itemset -> eggs) refers to the increase in the ratio of sale of "eggs" when itemset is sold.

So an itemset or antecedent with a lift of 1.4 has a 40% increased chance of being associated with the consequent "eggs". My question is: 40% increased chance increase compared to what? Not including them?