Sample size calculation for studies on temporomandibular disorders

Sample size calculation is a fundamental step for the validity and the usefulness
of results from a study. Nevertheless, as demonstrated by some papers in the
literature, such calculation is often ignored. Despite the lack of papers on this
topic, it is probable that this shortcoming also affects studies on
temporomandibular disorders. Therefore, the aim of this paper was to provide some
basic rules to calculate the sample size necessary for different types of
studies, both longitudinal and transversal, on those pathologies. Some examples
of the application of such rules for different types of studies have also been
provided, in order to make a full comprehension easier. In fact, the systematic
application of those rules is strongly requested for the effective usefulness of
results. Furthermore, an analysis of the statistical power of past studies on
temporomandibular disorders could be useful to evaluate if our epidemiological
and clinical-therapeutic knowledge of temporomandibular disorders is effectively
based upon studies conducted with the appropriate sample size.