Sample size calculator for reliability and validity evaluation: a Shiny R application.

OBJECTIVES: The objective is to provide a user-friendly tool for researchers to compute sample sizes for studies involving psychometric reliability and validity metrics. METHODS: The application was developed using R Shiny to create an interactive interface to calculate sample sizes for reliability, validity, and group difference assessments. For metrics already included in existing tools, cross-validation was performed to ensure consistency and accuracy. For metrics unique to this app, validation was based on formulas from the original publications. RESULTS: A comprehensive set of sample size calculation modules was included, covering Pearson correlation, Spearman correlation, tetrachoric correlation, point-biserial correlation, Cohen's kappa, Fleiss' kappa, Cronbach's alpha, intraclass correlation coefficient, Kendall's coefficient of concordance, one-way analysis of variance, and one-way analysis of covariance. Researchers can access detailed outputs, including sample sizes, contextual interpretations, and step-by-step derivations of the results, ensuring transparency and usability. CONCLUSIONS: The Sample Size Calculator is a validated and helpful resource for researchers seeking to optimize study design. The calculator can be accessed at the following website: https://biostats-shinyr.kumc.edu/PsychometricN/.