Thinking critically about information on the Web Available to Purchase

In addition to the obvious problems of precision and recall in relation to information retrieval via the Worldwide Web, the data retrieved may be inaccurate or out of date, even if the sites or resources located initially seem relevant. In response, a number of services have been developed over the lnternet which attempt to assist Web searchers in locating relevant, quality resources. Different approaches have been adopted, including the development of gateway services, reviewing resources and the allocation of numerical ratings. However, the effectiveness of the approach, and the quality of the ‘annotations’ used by these sites, can vary enormously. Using a specific medical Web resource, a number of services are compared to illustrate some of these issues, to introduce readers to the need to evaluate Web resources, and to provide some guidelines for evaluating the evaluative services. This article forms part of the work by the Advisory Group on Evaluation Criteria for Organising Medical Networked Information (OMNI), the eLib‐funded subject gateway for biomedicine. An earlier article compares and contrasts the facilities offered by a wider range of evaluative services.