aucRoc in caret package [SEC=UNCLASSIFIED]

David,

The ROC curve should really be computed with some sort of numeric data
(as opposed to classes). It varies the cutoff to get a continuum of
sensitivity and specificity values.  Using the classes as 1's and 2's
implies that the second class is twice the value of the first, which
doesn't really make sense.

Try getting the class probabilities for predicted1 and predicted2 and
use those instead.
Yes. You should be addressing this to Jin. I have been trying with  
little success to explain this.
David.
>
> Thanks,
>
> Max
>
>
> On Wed, Jun 1, 2011 at 9:24 PM, <Jin.Li at ga.gov.au> wrote:
>>
>> Please note that predicted1 and predicted2 are two sets of  
>> predictions instead of predictors. As you can see the predictions  
>> with only two levels, 1 is for hard and 2 for soft. I need to  
>> assess which one is more accurate. Hope this is clear now. Thanks.
>> Jin
>>
>> -----Original Message-----
>> From: David Winsemius [mailto:dwinsemius at comcast.net]
>> Sent: Thursday, 2 June 2011 10:55 AM
>> To: Li Jin
>> Cc: R-help at r-project.org
>> Subject: Re: [R] aucRoc in caret package [SEC=UNCLASSIFIED]
>>
>> Using AUC for discrete predictor variables with inly two levels
>> doesn't seem very sensible. What are you planning to to with this
>> measure?
>>
>> --
>> David.
>>
>> On Jun 1, 2011, at 8:47 PM, <Jin.Li at ga.gov.au> <Jin.Li at ga.gov.au>  
>> wrote:
>>
>>> Hi all,
>>> I used the following code and data to get auc values for two sets of
>>> predictions:
>>>            library(caret)
>>>> table(predicted1, trainy)
>>>   trainy
>>>    hard soft
>>>  1   27    0
>>>  2   11   99
>>>> aucRoc(roc(predicted1, trainy))
>>> [1] 0.5
>>>
>>>
>>>> table(predicted2, trainy)
>>>   trainy
>>>    hard soft
>>>  1   27    2
>>>  2   11   97
>>>> aucRoc(roc(predicted2, trainy))
>>> [1] 0.8451621
>>>
>>> predicted1:
>>> 1 1 2 2 2 1 2 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 1 2
>>> 2 2 2 2 1 2 2 2 2 1 1 2 2 2 2 2 1 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2
>>> 2 2 2 1 2 2 2 2 2 2 2 1 2 2 2 2 2 1 1 1 2 2 1 1 1 2 2 2 2 2 1 1 2 2
>>> 2 2 2 2 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  
>>> 2 2
>>>
>>> predicted2:
>>> 1 1 2 1 2 1 2 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 2 2 2 1 1 2
>>> 2 2 2 2 1 2 2 2 2 1 1 2 2 2 2 2 1 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2
>>> 2 2 2 1 2 2 2 2 2 2 2 1 2 2 2 2 2 1 1 1 2 2 1 1 1 2 2 2 2 2 1 1 2 2
>>> 2 2 2 2 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  
>>> 2 2
>>>
>>> trainy:
>>> hard hard hard soft soft hard hard hard hard soft soft soft soft
>>> soft soft hard soft soft soft soft soft soft hard soft soft soft
>>> soft soft soft soft soft soft hard soft soft soft soft soft hard
>>> soft soft soft soft hard hard soft soft soft hard soft hard soft
>>> soft soft soft soft hard soft soft soft soft soft soft soft soft
>>> hard soft soft soft soft soft hard soft soft soft soft soft soft
>>> soft hard soft soft soft hard hard hard hard hard soft soft hard
>>> hard hard soft hard soft soft soft hard hard soft soft soft soft
>>> soft hard hard hard hard hard hard hard soft soft soft soft soft
>>> soft soft soft soft soft soft soft soft soft soft soft hard soft
>>> soft soft soft soft soft soft soft
>>> Levels: hard soft
>>>
>>>> Sys.info()
>>>                     sysname
>>> release                      version                     nodename
>>>                   "Windows"                      "XP"        "build
>>> 2600, Service Pack 3"        "PC-60772"
>>>                     machine
>>>                       "x86"
>>>
>>> I would expect predicted1 is more accurate that the predicted2. But
>>> the auc values show an opposite. I was wondering whether this is a
>>> bug or I have done something wrong.  Thanks for your help in  
>>> advance!
>>>
>>> Cheers,
>>>
>>> Jin
>>> ____________________________________
>>> Jin Li, PhD
>>> Spatial Modeller/Computational Statistician
>>> Marine & Coastal Environment
>>> Geoscience Australia
>>> GPO Box 378, Canberra, ACT 2601, Australia
>>>
>>> Ph: 61 (02) 6249 9899; email:
>>> jin.li at ga.gov.au<mailto:jin.li at ga.gov.au>
>>> _______________________________________
>>>
>>>
>>>
>>>       [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> David Winsemius, MD
>> West Hartford, CT
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
>
> Max

David Winsemius, MD
West Hartford, CT

aucRoc in caret package [SEC=UNCLASSIFIED]

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