The Parametric Description of Retrieval Tests

Some parameters and techniques in use for describing the results of tests on IR systems are analysed. Several considerations outside the scope of the usual 2 x 2 table are relevant to the choice of parameters. In particular, a variable which produces a ‘performance curve’ of a system corresponds to an extension of the 2 x 2 table. Also, the statistical relationships between parameters are all‐important. It is considered that precision is not such a useful measure of performance (in conjunction with recall) as fallout. A more powerful alternative to Cleverdon's ‘inevitable inverse relationship between recall and precision’ is proposed and justified, namely that the recall‐fallout graph is convex.