THE RELATIONSHIP BETWEEN DOCUMENTS READ AND RELEVANT REFERENCES RETRIEVED AS EFFECTIVENESS MEASURES FOR INFORMATION RETRIEVAL SYSTEMS

The nature and relative merits of two measures of information retrieval system effectiveness, documents read and relevant references retrieved, are discussed. Using data on 2,380 searches completed at London University's Central Information Service, the author presents a mathematical model for the relationship between these two variables. Data suggest that this is best modelled by a monotonically asymptotic function, i.e. by a function increasing to a limit. A negative exponential function provides the best fit to the data, though a simpler hyperbolic function also provides a good fit. The suggested relationship between documents read and relevant references retrieved is further confirmed when the data is analysed by subject area of the user group. The major distinction between groups was the limiting value for mean number of documents read. Medical scientists read considerably more than the average, while engineers read considerably less. Biological, physical and social scientists were indistinguishable from the population as a whole within the statistical limitations of the data. Potential areas for further research are suggested.