Σύγκριση μεθόδων

	Μέγεθος Επίδρασης	Τιμή p και Στατιστική Σημαντικότητα
Πεδίο	Ερευνητική Στατιστική	Ερευνητική Στατιστική
Οικογένεια	Process / pipeline	Process / pipeline
Έτος προέλευσης	1988	1925
Δημιουργός	Jacob Cohen	Ronald Fisher
Τύπος	Concept	Concept
Θεμελιώδης πηγή	Cohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences (2nd ed.). Lawrence Erlbaum Associates. ISBN: 0-8058-0283-5	Fisher, R. A. (1925). Statistical Methods for Research Workers. Oliver and Boyd.
Εναλλακτικές ονομασίες	ES, Cohen's d, standardized effect, practical significance	p-value, significance test, statistical significance, alpha level
Συναφείς	4	5
Σύνοψη	Effect size quantifies the magnitude of a research finding independent of sample size. While a p-value tells you whether a result is statistically significant, an effect size tells you how big the result is. Jacob Cohen formalized effect size measurement in behavioral sciences (1988), establishing standard benchmarks (small = 0.2, medium = 0.5, large = 0.8 for Cohen's d). Effect sizes are essential for meta-analysis, power analysis, and communicating the practical importance of research findings.	The p-value is the probability of observing data as extreme as or more extreme than what was actually observed, assuming the null hypothesis is true. Introduced by Ronald Fisher in 1925, it is the foundation of frequentist hypothesis testing. Statistical significance is declared when the p-value falls below a pre-specified threshold (alpha level, typically 0.05).