3
$\begingroup$

I'm a developer and I've being playing around with R association rules to create a recommendation system. My stats understanding is a little basic. So I've created a set of rules with varying levels of confidence and I can use this to make predictions. However what I thought would be interesting would be to design a report a little like Excel's Shoppimg Basket analysis looking at the baskets and show their total value (i.e. basket occurence * value).

If I took the left hand side and right side of the rules generated by e.g. The rules with 0.8 confidence or higher. What in basic terms is that. Is it the most likely basket?

$\endgroup$
  • $\begingroup$ You need to consider both values: "Support" and "Confidence". In the other words "lift" give you a better insight about the importance of a rule. As an example: you have only one observation that someone that bought milk also bought cheese. You do not have any other observation about milk and cheese. In this scenario your confidence is 1 but this rule can not be very reliable because you have only 1 support that back your rule. $\endgroup$ – MFR Oct 13 '16 at 23:07
  • $\begingroup$ Ok so is support the number of times a rule occurs. Where does lift fit into this? Cheers. $\endgroup$ – MininallyExceptional Oct 13 '16 at 23:10
  • $\begingroup$ Support indicates the frequency of a rule. Lift shows how much an antecedent increase the probability of the consequence. We can say if a lift is greater than 1 the antecedent positively affect the consequence. The more is better, we can say , for example, if lift is 1.25 the antecedent increase the probability of occurrence of the consequence by 25% . $\endgroup$ – MFR Oct 13 '16 at 23:16
  • $\begingroup$ Right. So in my particular case I'd like to examine the most popular baskets. I guess the highest support is the number to sort by. Would it be fair to say the left hand combined with the right hand would be the whole basket? $\endgroup$ – MininallyExceptional Oct 13 '16 at 23:26
  • $\begingroup$ That's true. You can say their combination is the whole basket and support shows the most popular baskets. but again be careful about the interpreting the results. You might have some baskets with high supports with low confidence. It means, although the left hand item happened many times with the right hand one but it is very likely that the left hand one occur with the other items, as well. $\endgroup$ – MFR Oct 13 '16 at 23:30
2
$\begingroup$

An association rule is an an implication of expression of the form $X$ results in $Y$ and the strength of an association rule can be measured in terms both values:Support and Confidence. Both of them are great metrics but can cause some confusion. Support is important because a rule that has low support may occur by chance. Confidence measure the reliability of the inference made by rule. In the other words Lift give you a better insight about the importance of a rule.

Lift shows how much an antecedent increase the probability of the consequence. We can say if a lift is greater than 1 the antecedent positively affect the consequence. The more is better, we can say , for example, if lift is 1.25 the antecedent increase the probability of occurrence of the consequence by 25%

In your example, you can say the combination of the right hand and left hand items is the whole basket and support indicates the most popular baskets. But again be careful about the interpreting the results. You might have some baskets with high supports with low confidence. It means, although the left hand item happened many times with the right hand one, it is very likely that the left hand one occur with the other items, as well.

I don't go to mathematics behind them since they are very simple.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.