title: Type II error and statistical power in reports of small animal clinical trials.
abstract: OBJECTIVE
  To describe reporting of key methodological elements associated with type II error in published reports of small animal randomized controlled trials (RCTs) and to determine the statistical power in a subset of RCTs with negative results.
  
  
  METHODS
  Descriptive literature survey.
  
  
  METHODS
  Reports of parallel-group clinical RCTs published in 11 English-language veterinary journals from 2005 to 2012.
  
  
  METHODS
  Predefined criteria were used to identify trial primary outcomes and classify results as negative or positive. Details of sample size determination and use of confidence intervals in results reporting were recorded. For each 2-group RCT with negative results, the statistical power to detect 25% and 50% relative differences in outcome was calculated.
  
  
  RESULTS
  Of 238 RCTs, 42 (18%) stated a primary outcome, 52 (22%) reported a sample size calculation, and 18 (9%) included a confidence interval around the observed treatment effect. Reports of only 2 (0.8%) RCTs included all 3 elements. Among 103 two-group RCTs with negative results, only 14 (14%) and 40 (39%) were sufficiently powered (β < 0.20) to detect 25% and 50% relative differences in outcome between treatments, respectively.
  
  
  CONCLUSIONS
  The present survey found that small animal RCTs with negative results were often underpowered to detect moderate-to-large effect sizes between study groups. Information needed for critical appraisal was missing from most reports. The potential for clinicians to base treatment decisions on inappropriate interpretations of RCTs was worrisome. Design and reporting of small animal RCTs must be improved.
authors.affiliation: Department of Clinical Studies-Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Giuffrida
mesh_terms: D000818:Animals; D003627:Data Interpretation, Statistical; D011643:Publishing / Q000592:standards; D016032:Randomized Controlled Trials as Topic / Q000662:veterinary*; D012107:Research Design; D018401:Sample Size; D013223:Statistics as Topic; D014730:Veterinary Medicine / Q000379:methods*