Calculation and Justification of Sample Size in Researches of Psychological Sciences: Application of G*Power Software

Appropriate sample size calculation, its justification, and power analysis are too difficult in psychological sciences. The process of sample size calculation and power analysis using statistical formulas, especially without any background is too difficult. The informativeness of research depends on this justification. The more collected data, the more informativeness according to its inferential goals. In this paper, basic concepts have been discussed and then, G*Power software was briefly introduced for sample size determinations and power analysis. Briefly, 3 practical examples of the sample size calculations using this software were finally introduced. This software supports sample size calculation and power analysis for various statistical methods including exact test, t-tests, F-tests, Chi-Square tests, and Z-tests, each of these family tests includes many statistical tests. This software is user-friendly and useful software for estimating sample size and power analysis in psychological science research. This paper provides insight for a psychological researcher and it will make the researcher able to apply this software to other statistical tests