![]() ![]() The developers have a tutorial on using G*Power, but it is sparse in some places and may be difficult for some people to follow. Terms of use and a downloadable zip file are available here.Īfter downloading the program you may ask yourself, how do I use it? There are limited resources. Best of all, it is free! The developers released version 3.1.9 in 2014. It offers a wide variety of calculations along with graphics and protocol statement outputs. G*Power was created by faculty at the Institute for Experimental Psychology in Dusseldorf, Germany. I have used several power and sample size programs. My favorite is G*Power. Unfortunately many free programs are limited in the number of available power calculations. There are also several freeware power and sample size calculators available online. These programs are very good and will cost you about $1000. There are a number of commercial power and sample size programs available. Nowadays many institutional review boards (IRBs) and granting agencies require power and sample size calculations. Underpowered studies may have led investigators to incorrectly conclude that there were no effects from manipulations of their predictor/independent variables. Many had only a 20-30% chance of correctly rejecting the null hypotheses. Research has shown that a few decades ago studies in the social and health sciences were underpowered. Low statistical power may lead one to conclude that there is no effect from a treatment when there is (called a Type II error), while an “overpowered” study may lead one to conclude that a significant effect has practical or clinical significance when it does not.Ĭoncern over statistical power is a relatively recent phenomenon. It is important to know statistical power before launching a research project. Statistical power refers to the probability of correctly rejecting the null hypothesis of no effect. It goes something like this: “Hey McFly! That research won’t work on wishful thinking, unless you’ve got statistical power!” Hey, McFly! Those boards don’t work on water! Unless you’ve got power! This statement by Griff's buddies on Back to the Future II is applicable to the research domain. ![]()
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