On selecting a measure of retrieval effectiveness part II. Implementation of the philosophy

It was argued in Part I (see JASIS, March‐April 1973 p. 87) that the best way to evaluate a retrieval system is, in principle at least, to elicit subjective estimates of the system's utility to its users, quantified in terms of the numbers of utiles (e.g. dollars) they would have been willing to give up in exchange for the privilege of using the system; and a naive methodology was outlined for evaluating retrieval systems on this basis. But the impracticality of the naive evaluation procedure as it stands raises the questions: How can one decide which practical measure is likely to yield results most closely resembling those of the naive methodology? And how can one tell whether the resemblance is close enough to make applying the measure worth while? In the present paper two kinds of solution to these problems are taken up. The first answers the questions in terms of the reasonableness of the simplifying assumptions needed to get from the naive measure to the proposed substitute. The second answers it by experimentation.