Power/Sample Size in 1-Way Random-Effect Model

A macro is available for this purpose. For sample size (or group size or significance level) determination, the popular Brent method is employed for finding root of the form h(x) = 0.

Get The Macro

Obtain the macro from orempower.MAC. Place the macro under MACROS subfolder in MINITAB folder.

Run The Macro

Do EditCommand Line Editor:

(power04.png here)

Session Output

Executing from file: C:\Program Files\MINITAB 14\MACROS\orempower.MAC
 
Data Display

n    12.5432

Alternatively you can enable commands in session window by first clicking within the session window and then doing EditorEnable Commands. This is to 'switch on' the session command printing. Next time you do the process, the session command printing will be 'switched off'.

Session Output

MTB > # Find actual power when the common sample size is set at 13.
MTB > %orempower 50 10;
SUBC> groups 3;
SUBC> size 13.
Executing from file: C:\Program Files\MINITAB 14\MACROS\orempower.MAC
 
Data Display

power
   0.951878

MTB > # Find common sample size when group = 6.
MTB > %orempower 50 10;
SUBC> groups 6;
SUBC> power 0.95.
Executing from file: C:\Program Files\MINITAB 14\MACROS\orempower.MAC
 
Data Display

n    2.82234

MTB > # Find significance level when all other are set at respective
MTB > # values as specified.  Note that the significance level must
MTB > # be set at missing to accomplish this.
MTB > %orempower 50 10;
SUBC> groups 6;
SUBC> size 3;
SUBC> siglevel '*';
SUBC> power 0.95.
Executing from file: C:\Program Files\MINITAB 14\MACROS\orempower.MAC
 
Data Display

alpha    0.0375082

MTB > # Find groups (number of groups) when all others are set.
MTB > # Note that the significance level is at its default value (0.05).
MTB > %orempower 50 10;
SUBC> size 3;
SUBC> power 0.95.
Executing from file: C:\Program Files\MINITAB 14\MACROS\orempower.MAC
 
Data Display

groups    5.69228

MTB > # Power calculation when significance level is set at 0.01
MTB > # all other values are set.
MTB > %orempower 50 10;
SUBC> groups 6;
SUBC> size 3;
SUBC> siglevel 0.01.
Executing from file: C:\Program Files\MINITAB 14\MACROS\orempower.MAC
 
Data Display

power
   0.893596

Store Power Values

Suppose that the between variances are set at various values in C1 (named 'between') by:

(power05.png here)
Then do the following commands
name c2 'powers'
%orempower c1 1;
groups 6;
size 3;
power c2.
The power values will be stored in c2.

Scatterplot of powers vs between

Now do GraphScatterplot and select With Connected Line option. Then in the dialog box specify y and x variables (in main dialog box), title and subtitles (in Labels sub-dialog box), reference lines (in Scale sub-dialog box), and de-select symbols (in Data View sub-dialog box). When the graph popup, you can optionally edit the graphic elements by double click them and change them accordingly.

(power06.png here)