Introduction: We define the results list problem in information search and suggest the "associative index model", an ad-hoc, user-derived indexing solution based on Vannevar Bush's description of an associative indexing approach for his memex machine. We further define what selection means in indexing terms with reference to Charles Cutter's 3 objectives for the dictionary catalogue, particularly the selection objective. Method: A case study utilizing a structured-interview method illustrates and tests the feasibility of the model by comparing it the AquaBrowser's word cloud, a popular word association and visualization information retrieval system. Analysis: System-derived indexing schemes such as Aquabrowser's "word cloud" attempt to facilitate user processing of the results list by showing concept paths associated with the user's query. These externally-derived paths may not be helpful for an exploratory information search. The proposed model, which facilitates the user's information need processing, appears better suited for this type of search. Results: The case study provides anecdotal evidence indicating the potential benefits of the model over externally-derived indexing systems. Conclusion: Large-scale testing of the model is required to confirm the results. (Contains 2 tables and 5 figures.)