machine learning - How can I make Weka classify the smaller class, with a 2:1 class imbalance? -


how can make weka classify smaller classification? have data set positive classification 35% of data set , negative classification 65% of data set. want weka predict positive classification in cases, resultant model predicts instances negative classification. regardless, classifying negative (larger) class. how can force classify positive (smaller) classification?

one simple solution adjust training set more balanced (50% positive, 50% negative) encourage classification both cases. guess more of cases negative in problem space, , therefore need find way ensure negative cases still represent problem well.

since ratio of positive negative 1:2, try duplicating positive cases in training set make 2:2 , see how goes.


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