stats

confusion matrix (classifiers, diagnostic tests):

Actually positive Actually negative
Predicted positive True positive (TP) False positive (FP)
Predicted negative False negative (FN) True negative (TN)
Accuracy
How often was the prediction correct overall?
(TP + TN) / (TP + TN + FP + FN)
Precision / Positive Predictive Value (PPV)
Of the positive predictions, how many were right?
TP / (TP + FP)
Negative Predictive Value (NPV)
Of the negative predictions, how many were right?
TN / (TN + FN)
True positive rate (Recall / Sensitivity / Hit rate / Power)
Of the actual positives, how many did we find?
TP / (TP + FN)
True negative rate (Specificity)
Of the actual negatives, how many did we reject correctly?
TN / (TN + FP)
False positive rate (Fall-out)
FP / (FP + TN)
False negative rate (Miss rate)
FN / (FN + TP)