A general equation to consider, assuming α = 0.05 and β = 0.20, and a one-sided test (see Crawley: Statistics: An Introduction Using R. John Wiley & Sons (West Sussex, UK), p. 9, 2005 [ISBN 0470022981]), is: n ≈ (8 x s^2)/δ^2 where s^2 is the variance of the response and δ represents the difference […]