title: Understanding variation for clinical governance: an illustration using the diagnosis and treatment of sore throat.
abstract: BACKGROUND
  The aim of clinical governance is to improve clinical care. An understanding of the information contained in variation is central to any improvement effort. We must distinguish between variation intrinsic to a process (common cause variation) and variation caused by extrinsic factors (special cause variation). The control chart is a method of distinguishing between these two kinds of variation: it is used in industry to effect improvement and may be useful in primary care.
  
  
  OBJECTIVE
  To illustrate the use of control charts to distinguish between common cause and special cause variation and to guide appropriate action.
  
  
  METHODS
  Analysis of diagnostic and treatment decisions for sore throat.
  
  
  METHODS
  Single practice in the West Midlands.
  
  
  METHODS
  We identified each general practitioner's (GP's) consultations for sore throat over a two-year period. We grouped these into two diagnostic categories (tonsillitis and non-tonsillar throat infection) and two treatment categories (antibiotics and no antibiotics). These data were illustrated graphically as XY control charts.
  
  
  RESULTS
  In this practice, a special cause affects one GP's diagnosis--he is less likely to use the term 'tonsillitis'. A special cause also affects his treatment decisions--he is more likely to prescribe antibiotics. Diagnostic and treatment differences between the remaining GPs are consistent with common cause variation.
  
  
  CONCLUSIONS
  In this practice, action to improve the quality of diagnosis and treatment of sore throat shouldfocus on investigating why one practitioner's diagnosis and treatment differs from that of his colleagues. Control chart analysis is valuable because it enables users to obtain practical guidance for action.
authors.affiliation: Department of Public Health and Epidemiology, University of Birmingham, Edgbaston. T.P.Marshall@bham.ac.uk
authors.forename: Tom
authors.initials: T
authors.lastname: Marshall
authors.forename: Mohammed A
authors.initials: MA
authors.lastname: Mohammed
authors.forename: Hei Toon
authors.initials: HT
authors.lastname: Lim
mesh_terms: D003657:Decision Making; D004739:England; D005194:Family Practice / Q000592:standards*; D006801:Humans; D008485:Medical Audit / Q000379:methods*; D010612:Pharyngitis / Q000175:diagnosis* / Q000628:therapy; D017410:Practice Guidelines as Topic; D010818:Practice Patterns, Physicians' / Q000592:standards*; D011785:Quality Assurance, Health Care