[R] Analyzing Poor Performance Using naiveBayes()

[C.H.]

I think you have been hit by the problem of high variance. (overfitting)

Maybe you should consider doing a feature selection perhaps using the
chisq ranking from FSelector.

And then training the Naive Bayes using the top n features (n=1 to
200) as ranked by chisq, plot the AUCs or F1 score from both training
set and cross training set against n. From the graph, you can select
the optimal number of n.


On Fri, Aug 10, 2012 at 6:40 AM, Kirk Fleming <kirkrfleming at hotmail.com> wrote:
> My data is 50,000 instances of about 200 predictor values, and for all 50,000
> examples I have the actual class labels (binary). The data is quite
> unbalanced with about 10% or less of the examples having a positive outcome
> and the remainder, of course, negative. Nothing suggests the data has any
> order, and it doesn't appear to have any, so I've pulled the first 30,000
> examples to use as training data, reserving the remainder for test data.
>
> There are actually 3 distinct sets of class labels associated with the
> predictor data, and I've built 3 distinct models. When each model is used in
> predict() with the training data and true class labels, I get AUC values of
> 0.95, 0.98 and 0.98 for the 3 classifier problems.
>
> When I run these models against the 'unknown' inputs that I held out--the
> 20,000 instances--I get AUC values of about 0.55 or so for each of the three
> problems, give or take.  I reran the entire experiment, but instead using
> 40,000 instances for the model building, and the remaining 10,000 for
> testing. The AUC values showed a modest improvement, but still under 0.60.
>
> I've looked at a) the number of unique values that each predictor takes on,
> and b) the number of values, for a given predictor, that appear in the test
> data that do not appear in the training data.  I can eliminate variables
> that have very few non-null values, and those that have very few unique
> values (the two are largely the same), but I wouldn't expect this to have
> any influence on the model.
>
> I've already eliminated variables that are null in every instance, and
> duplicate variables having identical values for all instances. I have not
> done anything to check further for dependant variables, and don't know how
> to.
>
> Besides getting a clue, what might be my next best step?
>
>
>
>
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