Select the Quick tab of the Independent Sample t-Test: Sample Size Parameters dialog box to access options to establish the basic parameters for analyzing sample size for the independent sample t-test.

Fixed Parameters. The entries in the boxes under Fixed Parameters specify the fixed, or baseline, parameters for subsequent power calculations and graphs. Parameters that are not varied explicitly as the independent (X-axis) variables in a graphical analysis will be set equal to these values.

Mu1. In the Mu1 box, enter the mean for the population from which group 1 was sampled.

Mu2. In the Mu2 box, enter the mean for the population from which group 2 was sampled.

Alpha. In the Alpha box, enter the Type I error rate used in determining the critical value for the t-statistic.

Sigma. In the Sigma box, enter the common population standard deviation for the populations sampled from in the analysis.

Power Goal. In the Power Goal box, enter the minimum acceptable power, for which a minimum sample size is calculated. If the search for an acceptable sample size is successful, the actual power of the statistical test will be greater than or equal to this value.

Type of Hypothesis. Use the options buttons under Type of Hypothesis to determine the type of null hypothesis tested by the t-statistic.

2-tailed (Mu1 = Mu2). Select the 2-tailed (Mu1 = Mu2) option button to use null and alternative hypotheses of the form

H0: μ1 = μ2 H1: μ1 ¹ m2

1-tailed (Mu1 <= Mu2). Select the 1-tailed (Mu1 <= Mu2) option button to use null and alternative hypotheses of the form

H0: μ1 ≤ m2 H1: m1 > m2

1-tailed (Mu1 >= Mu2). Select the 1-tailed (Mu1 >= Mu2) option button to use null and alternative hypotheses of the form

H0: μ1 ³ m2 H1: m1 < m2