title: Potential errors and misuse of statistics in studies on leakage in endodontics.
abstract: OBJECTIVE
  To assess the quality of the statistical methodology used in studies of leakage in Endodontics, and to compare the results found using appropriate versus inappropriate inferential statistical methods.
  
  
  METHODS
  The search strategy used the descriptors 'root filling' 'microleakage', 'dye penetration', 'dye leakage', 'polymicrobial leakage' and 'fluid filtration' for the time interval 2001-2010 in journals within the categories 'Dentistry, Oral Surgery and Medicine' and 'Materials Science, Biomaterials' of the Journal Citation Report. All retrieved articles were reviewed to find potential pitfalls in statistical methodology that may be encountered during study design, data management or data analysis.
  
  
  RESULTS
  The database included 209 papers. In all the studies reviewed, the statistical methods used were appropriate for the category attributed to the outcome variable, but in 41% of the cases, the chi-square test or parametric methods were inappropriately selected subsequently. In 2% of the papers, no statistical test was used. In 99% of cases, a statistically 'significant' or 'not significant' effect was reported as a main finding, whilst only 1% also presented an estimation of the magnitude of the effect. When the appropriate statistical methods were applied in the studies with originally inappropriate data analysis, the conclusions changed in 19% of the cases.
  
  
  CONCLUSIONS
  Statistical deficiencies in leakage studies may affect their results and interpretation and might be one of the reasons for the poor agreement amongst the reported findings. Therefore, more effort should be made to standardize statistical methodology.
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, University of Granada, Granada, Spain. clucena@ugr.es
authors.forename: C
authors.initials: C
authors.lastname: Lucena
authors.forename: J M
authors.initials: JM
authors.lastname: Lopez
authors.forename: R
authors.initials: R
authors.lastname: Pulgar
authors.forename: C
authors.initials: C
authors.lastname: Abalos
authors.forename: M J
authors.initials: MJ
authors.lastname: Valderrama
mesh_terms: D003627:Data Interpretation, Statistical; D003763:Dental Leakage; D004708:Endodontics / Q000592:standards*; D006801:Humans; D012107:Research Design / Q000592:standards; D058028:Research Report / Q000592:standards*; D013223:Statistics as Topic / Q000592:standards