Association Rule

 

1. Both X and Y can be placed on the same shelf, so that buyers of one item would be prompted to buy the other.
2. Promotional discounts could be applied to just one out of the two items.
3. Advertisements on X could be targeted at buyers who purchase Y.
4. X and Y could be combined into a new product, such as having Y in flavors of X.

Support: 

It says, how many times item occurred in all records.

ex. apples occurred 50% (0.5) times in all transactions.

* Confidence:

It says how many time both apple and beer are purchased whenever apple is purchased.

example. confidence = 0.75 

means 75% times apples and beer both purchased whenever apples are purchased.

means if 100 people purchased apple then out of 100, 75 people purchased apple with beer both and 

25% apple without beer.

One drawback of the confidence measure is that it might misrepresent the importance of an association. This is because it only accounts for how popular apples are, but not beers. If beers are also very popular in general, there will be a higher chance that a transaction containing apples will also contain beers, thus inflating the confidence measure. To account for the base popularity of both constituent items, we use a third measure called lift.

* Lift:

This says how likely item Y is purchased when item X is purchased, while controlling for how popular item Y is. In Table 1, the lift of {apple -> beer} is 1,which implies no association between items. A lift value greater than 1 means that item Y is likely to be bought if item X is bought, while a value less than 1 means that item Y is unlikely to be bought if item X is bought.