The post hoc estimation of power is also an option for determining sample size; this method, however, is used after a study has actually been carried out and involves the researcher interpreting the results and identifying the effect sample size and effect size have on the power (Stevens, 2009). Not all researchers and statisticians favour this method. Lenth (2001) cautions against retrospective planning such as the post hoc, stating that the goal of this method involves “collect[ing] enough additional data to obtain statistical significance, while ignoring scientific meaning” (p. 191).
Regardless of which sample size estimation method a researcher chooses, he or she must acknowledge that sample size, effect size, and power are dependent on one another and that in order to estimate or determine one, information about the other two is needed. A wealth of