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Decision trees

Posted by AliWasp

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AliWasp

Decision trees
November 03, 2010 09:37AM

Registered: 14 years ago
Posts: 16
Rating: 0

Hey can some one help me out with working out the gain with regards to decision trees, please. I'm looking at the exam paper example for 2010, question 5.2, How do we get firstly the 0,1 for the first I and then how do we go from the fractions in brackets to the next line???
ie how does 5/14 I(3/5,2/5) end up being 5/14.0.98??
I think I'm being really doff sad smiley

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brettc

Re: Decision trees
November 03, 2010 09:55AM

Registered: 16 years ago
Posts: 184
Rating: 0

The 0 and 1 in the first line is because there are 4 entries for Overcast, and all four of them have a YES Outlook. 0/4 = 0 & 4/4 = 1.

Then you have 5/4 * I(3/5, 2/5), you take the p value which is 3/5 = 0.6 go to the table in appendix A (at the end of the tut) find 0.6 and it gives you the value for I, which is 0.98.

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AliWasp

Re: Decision trees
November 03, 2010 10:01AM

Registered: 14 years ago
Posts: 16
Rating: 0

Ah ha! I see now!! Thank you so much I had figured out the p value part!! smiling smiley