IRE An experiment: search strategy variations in SDI profiles chapter Lynn Evans Butterworth & Company Karen Sparck Jones All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright holder, application for which should be addressed to the Publishers. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature. 14 An experiment: search strategy variations in SDI profiles Lynn Evans 14.1 Introduction This research project was one of a number concerned with mechanized information retrieval carried out at INSPEC and supported by grants from, originally, the Department of Education and Science's Office for Scientific and Technical Information (OSTI) and, later, the British Library Research and Development Department (BLRDD). The first project, in the period l967[OCRerr]9, had investigated the performance, economics and acceptability to users of a computerized SDI service in electronics1. As a result of this study, in 1970 INSPEC offered publicly an SDI service in electronics. Another research project2, overlapping the SDI investigation, had established the comparative effectiveness of natural language as a medium for mechanized searching so that, from 1971, all documents input to the INSPEC database were assigned free index terms. These are significant words and phrases from the title, abstract and text of the document, selected by the information scientists as representing the meaningful concepts treated in the document. In April 1971 the cost-recovery service in electronics was replaced by a commercial SDI service covering the whole of the INSPEC subject areas with the important addition that free indexing was now available as a search medium. In the original INSPEC SDI investigation an EJC-type thesaurus was used for document indexing and profile generation. The complete thesaurus was never produced in printed form and so was not available to users for compiling their own profiles. The introduction of free indexing removed this barrier and prompted another study3 into the optimum degree of user participation in SDI profile generation. This concluded that users prepared to familiarize themselves with the `mechanics' of the system compiled their own best profiles as measured by precision (although indirect evidence indicated lower recall values than in the profiles compiled by INSPEC staff). However subscribers were reluctant to become too involved in that 45 per cent of them chose to delegate profile compilation to INSPEC staff and only 14 per cent opted to completely manage their own profiles. The main reason offered in explanation was that users found the whole procedure of getting a 285