To determine the number of replicates needed to detect a ‘true’ difference between sample means use the following formula (Sokal and Rohlf, 1981 Biometry: The Principles and Practice of Statistics in Biological Research. W.H. Freeman & Co., New York. p 262, Box 9.13): N = 2(s/d)2 * {tα [v] + t2(1-P)[v]}2 where N=number of replications