Either a power table or technology can be used to determine power for a t test for independent means. The provided power table assumes equal sample sizes for each of the two groups. In terms of power, the harmonic mean of the numbers of participants in two unequal sample sizes gives the equivalent sample size for what would be had with two equal samples. The harmonic mean sample size is given by the formula below, where Upper N 1 is the first sample size and Upper N 2 is the second sample size. When using a table, if the harmonic mean is not present in the table, use the value in the "Number of Participants in Each Group" column that is closest to the actual harmonic mean. Harmonic MeanequalsStartFraction left parenthesis 2 right parenthesis left parenthesis Upper N 1 right parenthesis left parenthesis Upper N 2 right parenthesis Over Upper N 1 plus Upper N 2 EndFraction