High recall or precision for information retrieval system? For disease detection, we need a high recall.
For information retrieval system, do we need a high precision?

Disease detection is about more than just recall. For instance, perfect recall is possible by diagnosing everyone with everything. Then it becomes a balance of missing cases vs false diagnoses and what you value in a physician.
There is a similar issue with search engines. Is it okay to miss a bunch of pertinent results if the couple of shown results all are pertinent? This corresponds to perfect precision. Is it acceptable to show irrelevant results if you show all possible relevant results? This corresponds to perfect recall.
It will be essential to answer those questions.
Yes, we want our doctors and search engines to be perfect, but they are not. Their quality is judged by the infrequency of their mistakes and the severity of the consequences of those mistakes.
