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Validity issues in split‐mouth trials *
Author(s) -
Hujoel P. P.,
DeRouen T. A.
Publication year - 1992
Publication title -
journal of clinical periodontology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.456
H-Index - 151
eISSN - 1600-051X
pISSN - 0303-6979
DOI - 10.1111/j.1600-051x.1992.tb01709.x
Subject(s) - variance (accounting) , statistics , a priori and a posteriori , carry (investment) , computer science , mathematics , econometrics , medicine , philosophy , accounting , epistemology , finance , economics , business
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.