Sample size: Accepting an alpha risk of 0.05 and a beta risk of 0.2 in a bilateral contrast, 26 subjects were required in each group to detect a difference equal to or greater than 3 microvolts (Total of 78 subjects). It assumes a standard deviation of 4.8 microvolts and the rate of loss to follow up esteem 20% (Magalhães-Resende et al. 2012).