Only as good as their major reference source, Medline. But Medline is biased toward alternative medicine. I recently pointed out that Medline searches of topics related to Complementary and Alternative Medicine (CAM) were overwhelmingly uncritical. Why? According to this editorial by Wallace Sampson, the process of journal selection for Medline indexing is riddled with conflicts of interest.
He concludes: This situation has resulted in an advocacy-dominated fund of material that biases research reports, systematic reviews, and meta-analyses; alters student research projects and medical school teaching; and biases patient and physician searches.