title: Use of the limits of agreement approach in periodontology.
abstract: OBJECTIVE
  To discuss the statistical approaches that have been traditionally used to compare measures in periodontal research, highlighting its strengths and weaknesses and, finally, to suggest the use of the limits of agreement method of Altman and Bland (1983) as an alternative method to address this question.
  
  
  METHODS
  Using a sample dataset of clinical periodontal measures as a background, the different possible approaches for agreement assessment are discussed and statistical and clinical points are considered. Eight hundred and forty repeated measures, belonging to the training phase of a clinical study, were performed in five individuals presenting different severities of periodontal conditions. The use of correlation coefficient, comparison of means, linear regression technique, Kappa coefficient, intra-class correlation coefficient and means versus differences plot is demonstrated.
  
  
  RESULTS
  Most of the methods are applied without the appropriate care, resulting in misleading interpretations. The information that arises from some of the methods used so far is poorly informative and adds little understanding to the operational characteristics of the raters or instruments. Some of the resulting information from the correlation coefficient and kappa coefficient may even be false or not applicable for the entire range of possible values.
  
  
  CONCLUSIONS
  The graphical approach that plots differences against means, including the 95% limits of agreement estimated by the mean difference +/- 1.96 standard deviation of the differences is the most informative approach and its application should be considered for continuous clinical periodontal measures.
authors.affiliation: Centre for Addiction and Mental Health, Health Systems Research & Consulting Unit, 33 Russell Street, Tower - T308, Toronto, ON M5S 2S1, Canada. diego_bassani@camh.net
authors.forename: Diego Garcia
authors.initials: DG
authors.lastname: Bassani
authors.forename: Letícia Algarves
authors.initials: LA
authors.lastname: Miranda
authors.forename: Anders
authors.initials: A
authors.lastname: Gustafsson
mesh_terms: D018865:Dental Research; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008875:Middle Aged; D017622:Periodontal Attachment Loss; D010514:Periodontal Pocket; D010517:Periodontics / Q000706:statistics & numerical data*; D014894:Weights and Measures