Transform proportion function

To use this function, choose Calc > Calculator.

Conducts the Freeman-Tukey transformation to stabilize variance for binomial data. For example, you can transform attribute data so the assumptions of the regression or ANOVA model are met.

Syntax

FTP(Trials,Events)

Specify the number of Trials and the number of Events; each can be a column or stored constant. Trials must be a positive integer. Events must be an integer between 0 and the number of trials, inclusive.

Example

A software developer tracks the proportion of words understood by a voice recognition software in various audio samples. To stabilize the variance and normalize the distribution of the data before performing regression or ANOVA, the developer transforms the proportion of the number events over the number of trials. The developer enters the expression FTP(C1,C2) and stores the results in C3.

C1 C2 C3
Total number of words (trial) Number of words understood (event) Transform Proportion
260 78 0.58047
160 24 0.40072
335 67 0.46476
100 22 0.49152
75 69 1.27422
525 273 0.80537

Formula

If you enter the number of trials (n) and the number of successes (x), Minitab transforms the data using the formula:

Bisgaard, Soren and Howard T. Fuller (1994) Quality Quandaries, Analysis of Factorial Experiments with Defects or Defectives as the Response, Quality Engineering, 7(2), 429–443.