Search filter precision can be improved by NOTing out irrelevant content.

BACKGROUND: Most methodologic search filters developed for use in large electronic databases such as MEDLINE have low precision. One method that has been proposed but not tested for improving precision is NOTing out irrelevant content. OBJECTIVE: To determine if search filter precision can be improved by NOTing out the text words and index terms assigned to those articles that are retrieved but are off-target.