Two Variances: Sample Size Parameters - Quick Tab

Select the Quick tab of the Two Variances: Sample Size Parameters dialog box to access options to establish the basic parameters for analyzing sample size for the F-test on two variances.

Fixed Parameters

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

Ratio

In the Ratio box, enter the ratio (Var1/Var2) of the two population variances assumed to hold in the populations being tested.

Alpha

In the Alpha box, enter the type I error rate (α) used in determining the critical value for the Chi-square statistic.

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 is greater than or equal to this value.

Type of Calculation

Use the options under Type of Calculation to specify which type of calculation to use in computing sample sizes. STATISTICA allows you to compute sample size in two types of situations: (1) where sample sizes are assumed to be equal, and (2) where one sample size is varied while the other is held constant.

Equal Df

Choose the Equal Df option button if sample sizes are assumed to be equal.

Vary Df1 (Fixed Df2)

Choose the Vary Df1 (Fixed Df2) option button to vary the degrees of freedom for the first sample, while holding degrees of freedom constant for the second sample.

Df2 =

In the Df2= box, enter the fixed value of Df2, if you are using the Vary Df1 (Fixed Df2) option.  Keep in mind that, unless the variance ratio is large or Df2 is large, an extremely large value of Df1 may be required to achieve desired power if you have selected the Vary Df1 (Fixed Df2) option. If the value is so large that program accuracy is compromised, you will be notified with an appropriate error message.

Type of Hypothesis

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

2-tailed (Var1 = Var2)

Select the 2-tailed (Var1 = Var2) option button to use the null and alternative hypotheses of the form

H₀: σ₁² = σ₂²    H₁: σ₁² ¹ s₂²

1-tailed (Var1 <= Var2)

Select the 1-tailed (Var1 <= Var2) option button to use the null and alternative hypotheses of the form

H₀: σ₁² ≤ σ₂²    H₁: σ₁² > σ₂²

1-tailed (Var1 >= Var2)

Select the 1-tailed (Var1 >= Var2) option button to use the null and alternative hypotheses of the form

H₀: σ₁² ³ s₂²    H₁: σ₁² < s₂²