To calculate a sample size for a hypothesis test about two means, specify the following quantities in the legacy calculator:
Alpha
The probability of a type I error, which is the probability of rejecting the null hypothesis when it is true. It is commonly referred to as the significance level of the test. The default alpha level is 0.05.
Std Dev
The assumed standard deviation where both groups are assumed to have equal standard deviation.
Extra Parameters
The number of parameters other than μ1 and μ2 in the hypothesis test. This option can be used for multi-factor designs. Leave the default zero in this field for simple cases.
In a multi-factor balanced design, the number of additional model parameters can be specified here. For example, in a three-factor two-level design with all three two-factor interactions, the number of additional parameters is four: one parameter for the other main effects, and three parameters for the interactions.
Specify two of the following parameters to calculate the third value, or specify one value to obtain a plot of the relationship between the other two parameters:
Difference to Detect
The smallest difference between the two means that you want to be able to declare statistically significant.
Sample Size
The total number of observations (runs, experimental units, or samples) in your experiment. Use half of this sample size in each group.
Power
The probability of rejecting the null hypothesis when it is false. With all other parameters fixed, power increases as sample size increases.
Continue
Evaluates the missing value when two parameters are specified, or launches a plot comparing two missing parameters if only one parameter is specified.
Back
Returns to the previous Sample Size and Power launch window.