- The classifier assigns the wrong class to a document, e.g. a class A page is classified as class B.
- The classifier fails to assign any class to a document.
- Precision is calculated by dividing the number of documents that were correctly assigned a particular class by the total number documents that were assigned that class.

- Recall is calculated by dividing the number of documents that were correctly assigned a particular class by the total number of documents of that class.

