Why is my Decision Tree have duplicate attributes in the same branch?Hi all. Just wondering if anybody knows why the decision tree is (in the case below) selecting Nozzle Air Pressure >42.09, then appears to contradict itself in the next node by selecting and splitting the Nozzle Air Pressure again? My understanding is that once an attribute is split, it should no longer be considered in subsequent branches. I'm using 10-fold cross validation with a holdback of 30%. I assume as I've both continuous and nominal data that JMP uses the CART algorithm?
AnalyticsRe: Why is my Decision Tree have duplicate attributes in the same branch?Hi @kom ,
I don't know the exact algorithm that JMP uses when splitting the decision trees, however, conceptually, it is working as intended and not contradicting itself. If you look at the other splits of your decision tree, you can see that other attributes are also used multiple times. What isn't used multiple times is the same value.
In your example, at the node where the air pressure is >=42, JMP is simply using that as a decision point to separate out the data. At the next node, JMP is saying that for all those instances where air pressure is >=42, it makes an additional split where the air pressure is still >=42, but is (>=42 and also <45) OR it's (>=42 and also >45).
How are you using BOTH 10-fold cross validation and a holdback of 30%. Typically, you would only use one type of validation method.
DS
Re: Why is my Decision Tree have duplicate attributes in the same branch?Hi Diedrich. Many thanks for taking the time to reply. Firstly, you are correct - in my speed to write the mail, I incorrectly wrote k-fold AND holdback. I did actually try both, and got somewhat similar results.
The Decision Tree follows the IF x AND y THEN z logic to classify the data. I get that it makes the 1st split at air pressure >=42, and I can accept that >=42 AND <45 makes sense now (in fact, this is the 1st time I've seen a decision Tree specify the same attribute to be between 2 values). Having said all that, being >=42 AND >=45 makes no practical sense at all. You agree?
Kieran
Re: Why is my Decision Tree have duplicate attributes in the same branch?I think that only you can determine if the split of 42 to 45 makes practical sense. But to understand multiple splits on the same variable, suppose you have a situation where the relationship between Y and X is linear. So, for example, we KNOW that Y=10+20*X. In the real world we would not know this true model, so if you fit a tree to data with this relationship, you will get multiple splits for X. It is the only way that the tree can try to mimic a continuous linear relationship.
Re: Why is my Decision Tree have duplicate attributes in the same branch?Oh, and what if it were a quadratic relationship? What do you think the tree splits would look like in that case?
