naive bayes accuracy increasing as increasing in the alpha value

Question

I'm using naive Bayes for text classification and I have 100k records in which 88k are positive class records and 12krecords are negative class records. I converted sentences to unigrams and bigrams using countvectorizer and I took alpha range from [0,10] with 50 values and I draw the plot.

In Laplace additive smoothing, If I keep increasing the alpha value then accuracy on the cross-validation dataset also increasing. My question is is this trend expected or not?

Answer 1

If you keep increasing the alpha value then naive bayes model will bias towards the class which has more records and model becomes a dumb model(underfitting) so by choosing small alpha value is good idea.