title: Considerations for the interpretation of findings from single and multiple studies of periodontal conditions.
abstract: This paper reviews considerations involved in the interpretation of results of individual periodontal clinical trials and the synthesis of findings of multiple studies. The purpose of each study must be considered, particularly whether it is an epidemiological investigation, prevention trial or therapeutic clinical trial. The definition of clear end-points, whether they be hygiene end-points associated with calculus and plaque or disease end-points that measure extent of gingivitis and periodontitis, is essential. Other statistical considerations include the following: adequate sample size, balanced design, use of covariates, issues of the appropriate sampling unit, and proper statistical analysis. Statistical issues that must be considered include the types of tests of hypotheses, use of multiple comparison procedures when more than two groups are involved, corrections for multiple testing and precise estimation of parameters with corresponding confidence intervals. When comparing across clinical trials, three sources of heterogeneity that must be considered are: treatments, diseases, and target populations. The technique of meta-analysis is described for the statistical interpretation of data arising from several trials. A meta-analysis is conducted for six dental clinical trials that evaluated a triclosan/copolymer formulation for the reduction of plaque, calculus or gingivitis. Results indicate that the first five studies, which were reported simultaneously, showed a common effect, i.e., that the formulation successfully reduced either plaque or calculus. When the sixth study, reported at a different time, was added to the analysis, the collection of studies did not satisfy the homogeneity assumption necessary for estimating a common effect size. This illustrates the importance of testing for homogeneity before pooling possibly dissimilar studies.
authors.affiliation: University of Texas, M.D. Anderson Cancer Center, Houston.
authors.forename: S
authors.initials: S
authors.lastname: Zimmerman
mesh_terms: D000704:Analysis of Variance; D002986:Clinical Trials as Topic / Q000379:methods / Q000706:statistics & numerical data*; D006801:Humans; D015201:Meta-Analysis as Topic; D015233:Models, Statistical; D010510:Periodontal Diseases / Q000628:therapy*; D015203:Reproducibility of Results; D012107:Research Design / Q000706:statistics & numerical data*; D012494:Sampling Studies