title: Crude versus case-mix-adjusted control charts for safety monitoring in thyroid surgery.
abstract: BACKGROUND
  Patient-safety monitoring based on health-outcome indicators can lead to misinterpretation of changes in case mix. This study aimed to compare the detection of indicator variations between crude and case-mix-adjusted control charts using data from thyroid surgeries.
  
  
  METHODS
  The study population included each patient who underwent thyroid surgery in a teaching hospital from January 2006 to May 2008. Patient safety was monitored according to two indicators, which are immediately recognisable postoperative complications: recurrent laryngeal nerve palsy and hypocalcaemia. Each indicator was plotted monthly on a p-control chart using exact limits. The weighted κ statistic was calculated to measure the agreement between crude and case-mix-adjusted control charts.
  
  
  RESULTS
  We evaluated the outcomes of 1405 thyroidectomies. The overall proportions of immediate recurrent laryngeal nerve palsy and hypocalcaemia were 7.4% and 20.5%, respectively. The proportion of agreement in the detection of indicator variations between the crude and case-mix-adjusted p-charts was 95% (95% CI 85% to 99%). The strength of the agreement was κ = 0.76 (95% CI 0.54 to 0.98). The single special cause of variation that occurred was only detected by the case-mix-adjusted p-chart.
  
  
  CONCLUSIONS
  There was good agreement in the detection of indicator variations between crude and case-mix-adjusted p-charts. The joint use of crude and adjusted charts seems to be a reasonable approach to increase the accuracy of interpretation of variations in outcome indicators.
authors.affiliation: Unité d'Étude des Pratiques Professionnelles, Hospices Civils de Lyon, Pôle d'Information Médicale Évaluation Recherche, 162 avenue Lacassagne, F-69424 Lyon Cedex 03, France. antoineduclos@yahoo.fr
authors.forename: Antoine
authors.initials: A
authors.lastname: Duclos
authors.forename: Nicolas
authors.initials: N
authors.lastname: Voirin
authors.forename: Sandrine
authors.initials: S
authors.lastname: Touzet
authors.forename: Pietro
authors.initials: P
authors.lastname: Soardo
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Schott
authors.forename: Cyrille
authors.initials: C
authors.lastname: Colin
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Peix
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Lifante
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D003953:Diagnosis-Related Groups; D005260:Female; D019538:Health Care Surveys; D006784:Hospitals, Teaching; D006801:Humans; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011446:Prospective Studies; D020379:Risk Adjustment; D017751:Safety Management; D013961:Thyroid Gland / Q000601:surgery*; D055815:Young Adult