More power to you: Simple power calculations for treatment effects with one degree of freedom.
Campbell, J.I.D. and Thompson, V.A.
Behavior Research Methods Instruments & Computers, 34(3), 332-337 (2002).
Although numerous computer programs for statistical power analysis are available, power is an underused aspect of experimental analysis, perhaps because of the perceived difficulty of performing the necessary calculations or because existing computer software can be expensive or complicated to learn. For single-degree-of-freedom tests, however, it is possible to calculate power in a straightforward manner, using the t distribution. Because these calculations are based on t, they use easily understood and readily available quantities. These calculations can be performed with a desk calculator; we also present a simple-to-use program called MorePower that will perform the necessary calculations. The straightforward nature of the calculations potentially will enable more researchers to consider issues of power when planning and reporting their experiments.