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.

Comparison of intervention effects in split-mouth and parallel-arm randomized controlled trials: a meta-epidemiological study

“…As compared with parallel-arm RCTs, split-mouth RCTs have the advantage that most of the variability of outcome among patients is removed from the intervention effect estimate for a potential increase in statistical power, each subject being its own control [4,5]. Because every subject receives each intervention, the design may also be better suited to determine patient preferences.…”

Comparative analysis of hyaluronan gel and xanthan-based chlorhexidine gel, as adjunct to scaling and root planing with scaling and root planing alone in the treatment of chronic periodontitis: A preliminary study

“…To overcome validity issues such as carry-over issues and asymmetric disease distribution[12] and to evaluate systemic/hematological inflammatory load due to periodontal disease and NSP treatment, whole mouth design was used for this study.…”

Sample size considerations for split-mouth design

“…6 In addition, some researchers pointed out that the split-mouth design can only be more efficient than the parallel-group design when the within-patient correlation coefficient is substantial, where efficiency is determined in terms of the number of measurements needed. 7 However, relatively little attention has been paid in literature to the sample size consideration for the split-mouth design and a rigorous comparison with the parallel-group design is not available. This paper intends to fill this gap by developing closed-form sample size formulas to help clinicians on effectively designing a split-mouth study.…”