Was used the "formula to calculate sample size when is expected to find an average difference and is known the standard deviation, given reliability and power (considering different variances)." A control ratio was established: cases of 1: 1, a level of significance or probability of error type 1 (α) of 0.05 (reliability of 95%) and a probability of error type 2 (β) of 0.20 (power of 80 %).