Two specific approaches of how to evaluate an information retrieval system are explored. The first is a mathematical model for use in studying how to minimize operating costs. The model provides a method for comparative evaluation between systems. The cost model divides the costs of a retrieval system into two components: system costs and user costs. The second approach is the development of a simulation model as a preliminary step toward the creation of a tool for system design and evaluation. The simulation program creates a well specified collection of documents and analyzes the effect of changes in query file characteristics on system performance. Employing the thesaurus, pseudo-documents and pseudo-queries are compared to see the effect of various query file parameter changes on the quantity of material retrieved. Evaluation of the simulation output indicates that there are small differences between the results of the experimental runs. It is concluded that one method for generating pseudo-queries is not clearly better than another. It is believed, however, that the simulation model as an approach to the evaluation of retrieval systems provides a limited but useful framework for the evaluation of information retrieval systems. (Author/MM)