I am trying to interpret the AUCPR. Say I have the following Precision-Recall curve.
It ends at
0.38 on the y-axis because this particular plot has slightly imbalanced data, so am I correct in thinking its the sum of the positive class / the sum of the negative class.
If I had a negative class of
26300 and a positive class of
10000 then the PR curve would stop at
10000 / 26300 = 0.38.
In regards to the AUCPR. I understand that perfect accuracy would be a straight line going along the top of the plot but if this curve had a AUCPR of
0.90 then it would be considered good, however how can I interpret it when the value is perhaps
0.50, this couldn´t be a random guess like in AUROC since the curve ends at
0.38. Is there a way to know when the model becomes worse than flipping a coin?