Two Correlations: Sample Size Calculation Results - Quick Tab

Select the Quick tab of the Two Correlations: Sample Size Calculation Results dialog box to access options to interactively view the results of sample size calculations and generate plots of required sample size as a function of quantities that affect sample size in practice.  

X-Axis Graphing Parameters

The entries in the boxes under X-Axis Graphing Parameters establish the start value, end value, and number of steps on the X-axis for the graphs specified under Sample Size Charts.

Start Rho1

In the Start Rho1 box, enter the starting value of rho1 used in the N vs. Rho1 sample size chart.

End Rho1

In the End Rho1 box, enter the final value of rho1 used in the N vs. Rho1 sample size chart.

Start Alpha

In the Start Alpha box, enter the starting value of alpha used in the N vs. Alpha sample size chart.

End Alpha

In the End Alpha box, enter the final value of alpha used in the N vs. Alpha sample size chart.

Start Power

In the Start Power box, enter the starting value of power goal used in the N vs. Power  sample size chart.

End Power

In the End Power box, enter the final value of power goal used in the N vs. Power  sample size chart.

No. of Steps.

In the No. of Steps box, enter the number of steps, or intervals, to plot on the X-axis in the charts specified in the Sample Size Charts group box.

Computational Algorithm

The Power Analysis module allows you to choose from two algorithms:

Fisher Z Refined

Select the Fisher Z Refined option button to employ an approximation based on the Fisher transformation, but using refined series approximation formulae for the mean and variance (Fouladi, 1991).

Fisher Z Crude

Select the Fisher Z Crude option button to use the traditional (somewhat crude) approximation, based on the Fisher transformation, assuming that the mean of the Fisher transform of r is the Fisher transform of r, and that the variance of the Fisher transform of r is 1/(N - 3).

N to Vary

Use the options under N to Vary to specify which sample size (if any) to vary when computing sample sizes and plotting charts. STATISTICA allows you to compute and plot 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 N

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

Vary N1

Choose the Vary N1 option button to vary the degrees of freedom for the first sample, while holding degrees of freedom constant (at N₂=100) for the second sample.

Vary N2

Choose the Vary N2 option button to vary the degrees of freedom for the second sample, while holding degrees of freedom constant (at N₁=100) for the first sample.

Sample Size Charts

Use the buttons under Sample Size Charts to produce charts of required N as a function of power goal, population correlation, or type I error rate.  Note that parameters given in the X-Axis Graphing Parameters box control the range of values plotted on the X-axis and the number of steps plotted.

N vs. Rho1.

Click the N vs. Rho1 button to produce a plot of sample size (N) versus the group 1 population correlation. The population correlation for the second group is held constant at the current fixed parameter value.

N vs. Alpha.

Click the N vs. Alpha button to produce a plot of sample size (N) vs. type I error rate.

N vs. Power.

Click the N vs. Power button to produce a plot of sample size (N) versus power goal.