Accuracy is the share of evaluated predictions that match the actual outcomes. For a classifier, it summarizes how often the model is correct overall. section 8.18
Measure it on examples the model has not seen during training: a score on training data can be misleading. Accuracy gives an overall view, so check other metrics when you need more detail about performance across classes. section 8.12 section 8.13 section 8.18
Diamond-cut predictions
In the ten-example test set, seven predicted cuts match the actual cuts, so the classifier is correct on seven of ten examples. section 8.18
Table 8.17 The diamond dataset for classification and predictions
|
Carat |
Price |
Cut |
Prediction |
||
| 1 |
0.26 |
689 |
Okay |
Okay |
✓ |
| 2 |
0.41 |
880 |
Perfect |
Perfect |
✓ |
| 3 |
0.52 |
1,012 |
Perfect |
Perfect |
✓ |
| 4 |
0.76 |
907 |
Okay |
Okay |
✓ |
| 5 |
0.81 |
2,650 |
Okay |
Okay |
✓ |
| 6 |
0.90 |
2,634 |
Okay |
Okay |
✓ |
| 7 |
1.24 |
2,999 |
Perfect |
Okay |
✗ |
| 8 |
1.42 |
3,850 |
Perfect |
Okay |
✗ |
| 9 |
1.61 |
4,345 |
Perfect |
Perfect |
✓ |
| 10 |
1.78 |
3,100 |
Okay |
Perfect |
✗ |
Compare each predicted diamond cut with its actual cut to see which examples count as correct. section 8.18































