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Validity issues in split-mouth trials.

Authors
Type
Published Article
Journal
Journal of Clinical Periodontology
0303-6979
Publisher
Wiley-Blackwell
Publication Date
Volume
19
Issue
9 Pt 1
Pages
625–627
Identifiers
PMID: 1430289
Source
Medline

Abstract

The main purpose of the split-mouth design is to remove all components related to differences between subjects from the treatment comparisons. By making within-patient comparisons, rather than between-patient comparisons, the error variance (noise) of the experiment can be reduced, thereby obtaining a more powerful statistical test. Unfortunately, comparisons made on a within-patient basis have potential disadvantages. Treatments may have effects on experimental units other than those which they were assigned to (carry-across effects). Such effects cannot be estimated from split-mouth data. Neither can treatment effects be estimated. The estimable parameter in a split-mouth design is the treatment effect plus the sum of all carry-across effects. Unless a priori knowledge indicates that no carry-across effects exist, reported estimates of treatment efficacy are potentially biased. In the design of split-mouth clinical trials, potential gain in precision should be carefully weighed against a potential decrease in validity.

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