Two Arm Normal Program

Two Arm Normal Sample Size and Power

Function

Two Arm Normal is a program to calculate either estimates of sample size or power for differences in means. The program allows for unequal sample size allocation between the two groups.

Program Code

The program is written in JavaScript.

Source

Rosner, B., Fundamentals of Biostatistics, Prindle, Weber and Schmidt, 1982.

The formulas are the classic two sample formulas for sample size and power for two sample normal problem with constant variance.

Input Items

The user is prompted for values to the following items. For items that have initial default values set, the values are given in parentheses.

One-sided or two-sided test

a, the significance level (.05)

m₁, the mean in Group 1

m₂, the mean in Group 2

s, the square root of variance

n₂/n₁, the sample size ratio of Group 2 to Group 1 (1)

1-b, the desired power for sample size estimation, or n, the total sample size for power estimation

Back to Two Arm Normal program.