| TABLE 4.1 Contingency Table |
| Relevant | Not Relevant | ||
 |  |  | |
| a | NRet is the number of retrieved documents. | ||
| b | NNRet is the number of documents not retrieved. | ||
| c | NRel is the number of relevant documents. | ||
| d | NNRel is the number of irrelevant documents. | ||
| e | NDoc is the total number of documents. | ||