title: Conceptualization of category-oriented likelihood ratio: a useful tool for clinical diagnostic reasoning.
abstract: BACKGROUND
  In the diagnostic reasoning process medical students and novice physicians need to be made aware of the diagnostic values of the clinical findings (including history, signs, and symptoms) to make an appropriate diagnostic decision. Diagnostic reasoning has been understood in light of two paradigms on clinical reasoning: problem solving and decision making. They advocate the reasoning strategies used by expert physicians and the statistical models of reasoning, respectively. Evidence-based medicine (EBM) applies decision theory to the clinical diagnosis, which can be a challenging topic in medical education.This theoretical article tries to compare evidence-based diagnosis with expert-based strategies in clinical diagnosis and also defines a novel concept of category-oriented likelihood ratio (LR) to propose a new model combining both aforementioned methods.
  
  
  CONCLUSIONS
  Evidence-based medicine advocates the use of quantitative evidence to estimate the probability of diseases more accurately and objectively; however, the published evidence for a given diagnosis cannot practically be utilized in primary care, especially if the patient is complaining of a nonspecific problem such as abdominal pain that could have a long list of differential diagnoses. In this case, expert physicians examine the key clinical findings that could differentiate between broader categories of diseases such as organic and non-organic disease categories to shorten the list of differential diagnoses. To approach nonspecific problems, not only do the experts revise the probability estimate of specific diseases, but also they revise the probability estimate of the categories of diseases by using the available clinical findings.
  
  
  CONCLUSIONS
  To make this approach analytical and objective, we need to know how much more likely it is for a key clinical finding to be present in patients with one of the diseases of a specific category versus those with a disease not included in that category. In this paper, we call this value category-oriented LR.
authors.affiliation: Evidence-Based Medicine & Critical Thinking Working Team, Endocrinology and Metabolism Research Institute, Tehran University of Medical Sciences, IR Iran.
authors.forename: Hamideh
authors.initials: H
authors.lastname: Moosapour
authors.forename: Mohsin
authors.initials: M
authors.lastname: Raza
authors.forename: Mehdi
authors.initials: M
authors.lastname: Rambod
authors.forename: Akbar
authors.initials: A
authors.lastname: Soltani
mesh_terms: D000328:Adult; D003210:Concept Formation; D003657:Decision Making; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D008962:Models, Theoretical; D011336:Probability; D011340:Problem Solving; D055815:Young Adult
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