A probability question...

[adam]

My target class represents 18% of my dataset. If I were to just randomly classify cases to the target class, what % of my target predictions were be correct?

[editor]

If you assign all cases to the non-target class, you will be on the average 82% correct, but it will be a useless prediction.

If you assign cases to the target class with
18% probability, then the probability of one prediction being correct is
is 0.18*0.18 + 0.82*0.82 = 0.7048,
so you will get about 70.5% correct predictions.

Lesson - percent correct is not useful without associated cost of the wrong
prediction.

[adam]

So overall, 70.48% of my predictions would be accurate, but what percentage of my target predictions would be accurate?