title: Efficiency of split-mouth designs.
abstract: The purpose of this paper is (1) to investigate the similarity of the amount, distribution, and severity of periodontal disease of the within-patient experimental units, (2) to estimate the relative efficiencies of split-mouth designs when compared to whole-mouth designs, and (3) to discuss how stratification on initial pocket depth can result in large differences in the power of the test-statistics in the different disease categories. Periodontal disease characteristics are not always homogeneously distributed over the within-patient experimental units and this heterogeneity can reduce the efficiency of split-mouth designs. In particular, if analyses are stratified on initial pocket depth, sites with an initial probing depth deeper than 6 mm may be small in number and asymmetrically distributed when compared to sites with an initial probing depth less than 6 mm. This may result in large differences of the power of the test statistics among the different disease categories and should lead to a careful interpretation of the statistical significance tests. When disease characteristics are symmetrically distributed over the within-patient experimental units and a sufficient number of sites is present per experimental unit, the split-mouth design can provide moderate to large gains in relative efficiency. In the absence of a symmetric disease distribution, whole-mouth clinical trials may be preferable.
authors: Department of Biologic and Material Sciences, School of Dentistry, University of Michigan, Ann Arbor 48109.
authors: P P
authors: PP
authors: Hujoel
authors: W J
authors: WJ
authors: Loesche
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D012534:Dental Scaling; D006801:Humans; D016014:Linear Models; D010512:Periodontal Index; D010514:Periodontal Pocket / Q000175:diagnosis / Q000473:pathology; D010518:Periodontitis / Q000175:diagnosis* / Q000473:pathology / Q000628:therapy; D011336:Probability; D012107:Research Design / Q000706:statistics & numerical data*; D012680:Sensitivity and Specificity; D014092:Tooth Root / Q000601:surgery