Association Rules algorithm [support,confidence]

# Association Rules algorithm [support,confidence]

• Saturday, December 16, 2006 3:17 PM

In assotiation rules each rule has a [support, confidence] part. In Microsoft Association Rules there is a [probability,importance] measure in each rule and importance can be greater that 1.

I found the following in msdn but i'm not sure if i understood correctly.

MINIMUM_PROBABILITY: Specifies the minimum probability that a rule is true. For example, setting this value to 0.5 specifies that no rule with less than fifty percent probability is generated.
The default is 0.4.

MAXIMUM_SUPPORT: Specifies the maximum number of cases in which an itemset can have support. If this value is less than 1, the value represents a percentage of the total cases. Values greater than 1 represent the absolute number of cases that can contain the itemset.
The default is 1.

My questions are
1) Can i explain the [probability,importance] in [support,confidence]? If yes, how?
2) What importance>1 means?

### All Replies

• Monday, December 18, 2006 8:49 AM

MS Association Rules still has [support, confidence] like any other AR implementation.  If you take a rule of the form

A -> B

Support is the number of times the itemset A occurs, and confidence is the probability that B occurs when A occurs.  Importance is a different measure that indicates the lift of the rule e.g. the increase in probability of the target over the probability of the target at random, which is why it can be greater than 1.

In the DM viewers, the support is indicated on the Itemset page.

• Monday, December 18, 2006 5:29 PM

If i have a rule A,B => C and an itemset A,B,C with support 2000 then the support of the rule is 2000? How can i calculate the confidence then?

• Tuesday, December 19, 2006 7:26 AM
Moderator

If your rule is A,B=>C then:

Confidence == Probability == Numberof(A,B,C) / Numberof(A,B)

• Tuesday, December 19, 2006 4:46 PM

That was very helpful thank you :)
• Thursday, December 21, 2006 2:14 PM

Hi all,

I am trying to make an algorithm that also takes into account how "important" an association rule is. I found that "importance" is something that I am missing.

Ho is  importance calculated ?

greetz,
Alex
• Friday, December 22, 2006 6:11 PM
Moderator

The formula, with some details, is discussed in this thread:

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=290186&SiteID=1

• Sunday, January 29, 2012 7:02 AM

In assotiation rules each rule has a [support, confidence] part. In Microsoft Association Rules there is a [probability,importance] measure in each rule and importance can be greater that 1.

I found the following in msdn but i'm not sure if i understood correctly.

MINIMUM_PROBABILITY: Specifies the minimum probability that a rule is true. For example, setting this value to 0.5 specifies that no rule with less than fifty percent probability is generated.
The default is 0.4.

MAXIMUM_SUPPORT: Specifies the maximum number of cases in which an itemset can have support. If this value is less than 1, the value represents a percentage of the total cases. Values greater than 1 represent the absolute number of cases that can contain the itemset.
The default is 1.