Development of evidence based guidelines requires people with clinical, public health, or other relevant expertise and judgments about the evidence. The evidence underpinning those judgments should be identified, selected, appraised, synthesised, and presented systematically and transparently. 1 2 3 But sometimes using evidence systematically and transparently can be challenging: evidence may be unpublished or indirect, diseases rare, contextual information missing, or resources limited. In these situations, obtaining evidence from experts can be efficient, and experts may be the only or main source of evidence.
Using experts as a source of evidence has several problems and may seem at odds with evidence based medicine. However, its goal is to use expertise wisely in the context of evidence. 4 We contend that there is a difference between evidence that comes from experts (expert evidence) and expert opinion, and argue that the way in which expert evidence is used in a guideline’s development has an important bearing on the robustness and trustworthiness of the guideline.
Evidence in this context can be defined as facts (actual or asserted) intended for use in support of a conclusion. 5 An opinion is a view or judgment formed about something, not necessarily based on facts. 6 For example, a patient might say: “I had prostate cancer detected by prostate specific antigen (PSA) screening and I am alive 10 years later.” That is evidence. It is not the same as saying: “PSA screening saved my life.” That is an opinion. Similarly, a clinical expert might say: “I operated on 100 patients with prostate cancer and none of them died from prostate cancer.” That is evidence. It is not …