Clever searching for evidence

New search filters can help to find the needle in the haystack

Do people who write about and propagate evidence based medicine use its principles properly? A paper in this week's BMJ and two other recent BMJ papers report on such authors' abilities to find the best evidence.1^–3 On the way, they have provided excellent search strategies, using filters they call “hedges” (as in hedging one's bets) that help to separate the wheat (scientifically strong studies of diagnosis, treatment, and systematic reviews) from the chaff (less rigorous ones) in one of the most frequently accessed medical literature databases, Medline.

Why is this important? We still often need to search large databases such as Medline to find original research data because reviews may not cover our questions, may be out of date, and may not be relevant enough to real clinical problems. Databases of primary research are staggeringly large (there are more than 12 million citations in Medline, and 7 million in Embase). Most research papers are written as communications from scientist to scientist and relatively few have immediate clinical relevance. Most of the remainder are not rigorous enough to warrant …