n4Studies: Sample Size Calculation for an Epidemiological Study on a Smart Device

Abstract

Objective: This study was to develop a sample size application (called “n4Studies”) for free use on iPhone and Android devices and to compare sample size functions between n4Studies with other applications and software.
Methods: Objective-C programming language was used to create the application for the iPhone OS (operating system) while javaScript, jquery mobile, PhoneGap, and state were used to develop it for Android phones. Other sample size applications were searched from the Apple app and Google play stores. The applications' characteristics and sample size functions were collected. Spearman’s rank correlation was used to investigate the relationship between a number of sample size functions and price.
Results: “n4Studies” provides several functions for sample size and power calculations for various epidemiological study designs. It can be downloaded from the Apple App and Google play store. Comparing n4Studies with other applications, it covers several more types of epidemiological study designs, gives similar results for estimation of infinite/finite population mean and infinite/finite proportion from GRANMO, for comparing two independent means from BioStats, for comparing two independent proportions from EpiCal application. When using the same parameters, n4Studies gives similar results to STATA, epical package in R, PS, G*Power, and OpenEpi.
Conclusion: “n4Studies" can be an alternative tool for calculating the sample size. It may be useful to students, lecturers and researchers in conducting their research projects.