[Introduction of a User-oriented Application for Biometrical Sample Size Calculation in Clinical and Epidemiological...

Clinical journals strongly recommend the use of confidence intervals to present study results, since these comprise both the statistical significance and the clinical relevance of a study's outcome. However, the mandatory sample size calculations performed during a study's planning stage are mostly reported via significance test-based approaches, as there are currently only a few methods available for planning approaches via confidence intervals. As a result, many articles show a mismatch between the planning (based on significance tests) and result presentation (based on confidence intervals). To overcome this gap, a user interface will be illustrated that offers the opportunity of sample size calculation both by means of significance tests and confidence intervals, with intuitive access for clinical researchers.

Estimating sample sizes via confidence intervals requires the predetermination of the interval's maximum width, whereas the calculation of sample sizes via significance test has the minimum requirement of the test's statistical power. The resulting sample size formulas are compatible for all practically relevant cases and mainly differ in the specification of the parameters "width" and "power". For the choice of a suitable statistical power, there are established reference values (usually 80 or 90%), while the calculation of sample size by means of confidence intervals is still difficult for clinical researchers, due to the unavailability of guidelines for the choice of the interval width. The application of both approaches is demonstrated by planning a clinical trial on the rotational stability of toric intraocular lenses with or without an implemented capsular tension ring.

A user interface was developed to implement both of the publicly accessible approaches for sample size calculation. The interface allows comparison of the approaches based on significance test and confidence interval and their interchangeability for a two-armed clinical trial design. The operator firstly chooses one of the approaches; then the necessary planning information is inputted and the calculated sample size per trial as well as the corresponding planning information for the other approach are provided.

The presented sample size tool enables an intuitively accessible way to calculate sample sizes both via significance tests and via confidence intervals for two-armed study designs.