G*Power for Macintosh, Version 2.1.2 September 1997

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Contents of this document:

(1) Installation and registration

(2) What G*Power does and how it works

(3) How to get G*Power (i.e., where to check for future
updates and versions for

other platforms)

(4) How to find help for using G*Power

(5) Address for correspondence

(6) Disclaimer

A more detailed description of the program and its background
is available

in printed form:

Erdfelder, E., Faul, F., & Buchner, A. (1996). GPower:
A general power

analysis program. Behavior Research Methods, Instruments,
& Computers,

28, 1-11.

This article should appear very soon.

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(1) Installation and registration

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There are two versions of G*Power:

G*Power PPC

is the version to use on Power Macintoshes.

G*Power 68K

should run on any 68K Macintosh using System 7 or higher.
It has also been tested

successfully on some Power Macintosh models on which
it runs in emulation mode.

Sorry, earlier system software versions are no longer
supporeted, and a special

verion of G*Power for 68K computers with a 68881 FPU
is also no longer available.

No special installation procedure is necessary to use
G*Power. Simply copy the

program to your harddisk. However, we recommend that
you install only the

version appropriate for your Macintosh. Remove the
other versions.

G*Power is free. You may to give the program to friends
and colleagues who might

find it useful.

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VERY IMPORTANT: If you want to include G*Power on a
Shareware or Freeware CD-ROM

you MUST ask the authors for permission. Contact us
under the address given

below.

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Note that there is an MS-DOS version of G*Power, so
if your friends and

colleagues use that platform, they can also work with
G*Power if they like (see

Section (3) of this file for the FTP site to check for
updates and the MS-DOS

version of G*Power).

We encourage you to let us know your complete address
(including your e-mail

address if possible) and the version of G*Power you
use. As a registered user,

you will be informed about future program revisions.
Your personal data will be

used for this purpose only. Please send this information
to:

Axel Buchner

FB I - Psychologie

Universität Trier

D-54286 Trier

Germany

E-mail: buchner@cogpsy.uni-trier.de

We also ask you to report any errors or problems encountered
with G*Power to the

address mentioned in Section (5) of this file.

What follows is a brief description of the program (it
takes no more than five

minutes to read it).

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(2) What it does and how it works

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G*Power performs high-precision statistical power analyses
for the most common

statistical tests in behavioral research, that is, t-,
F-, and Chi2-tests. The

power values obtained by "accuracy mode" calculations
of G*Power are correct up

to five significant digits at least. Although available
for taking a quick look

at a problem, we do not encourage "speed mode"
calculations because they are less

accurate.

G*Power computes

(a) power values for given sample sizes, effect sizes
and alpha-levels (post hoc

power analyses);

(b) sample sizes for given effect sizes, alpha-levels,
and power values (a priori

power analyses);

(c) alpha- and beta-values for given sample sizes, effect
sizes and

beta/alpha-ratios (compromise power analyses).

It also displays graphically the relation between any
two of the relevant

variables.

Note that in a priori power analyses, the resulting
sample size is

rounded to the next larger integer. Therefore, the
actual power of

these analyses is usually somewhat larger than the one
specified.

G*Power informs you how large the power of your test
actually is given

the calculated samplesize.

In addition, G*Power calculates for you the critical
value of the

relevant test statistic and the noncentrality parameter
of the

noncentral distribution of your test statistic.

----------------------- The "Analysis window" -----------------------

The "Analysis window" is used to specify the
information necessary for a

particular power analysis, and it displays the results
of the last analysis.

Click "Calculate" to perform a single analysis
for the Type of Power Analysis,

the Type of Test, and the parameters you specified.

Click "Calc ES" (where ES is d, r, f, f2,
or w, depending on the type of test

currently selected) to open a dialog in which you can
specify the values

necessary to calculate the effect size for your power
analysis from empirical

data (e.g., from published studies).

Click "Draw graph" to open a dialog in which
you can specify the values necessary

to display one parameter (e.g., the power) as a function
of another parameter

(e.g., the total sample size) over a range of values
(e.g., from 20 to 220

subjects) in the "Graph window".

If the "Graph window" is already open, you
can simply double-click this window to

open the dialog in which you can specify the graph parameters.

------------------------- The "Graph window" -------------------------

The "Graph window" can be used to display
one parameter (e.g., the power) as a

function of another parameter (e.g., the total sample
size) over a range of

values (e.g., from 20 to 220 subjects).

The header of the graph always specifies the type of
test, and the fixed values.

The note below the graph tells you what calculation
mode you used. Default is

"Accuracy mode" which is very accurate (up
to five significant digits at least)

but the price is that you will usually have to wait
a little longer until you see

a result. "Speed mode" calculations are fast
but they may not be very accurate

(particularly for 'extreme' values). If you selected
"Speed mode", do not trust

the results too much!

You can copy the graph using "Copy graph"
from the "Edit" menu and paste it into

your word processor or drawing program documents for
saving or editing the graph

information. Inside G*Power you cannot edit or save
a graph.

The scaling of the axes in the "Graph window"
depends on the size of the window,

so re-sizing the window may have the effect of a more
fine-grained scaling.

If the "Protocol (table)" option in the "Graph
dialog" is on, a table of the

values used to plot the graph is written to the Result
window. This table can be

imported into your favorite graphics package, either
via the clipboard or by

saving the table as a G*Power file (see below).

------------------------- The "Result window" -------------------------

If the "Result window" is open, all parameters
of all power analyses performed in

the "Analysis window" are recorded here.

The "Result window" is fully editable (using
the commands from the Edit menu).

You can either copy the values you need to the clipboard,
or you can save the

entire information of the "Result window"
to a G*Power file using the Save or

Save as commands from the File menu.

Double-clicking such a file launches G*Power and opens
the file so you can record

more analyses in it. However, because G*Power files
are of type TEXT, they may

also be opened from inside your favorite word processor
or graphics package.

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(3) How to get G*Power

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The most convenient way to get a copy of G*Power is
to download the program from

the public FTP server at the University of Trier, Germany.
This is where you

should check for updates and future releases, and for
versions for other

platforms of G*Power. However, we will also try to
make available updates and

future releases of the Macintosh version on an info-mac
archive near you.

There are two ways to access this server:

(I) Via WWW:

http://www.psychologie.uni-trier.de:8000/projects/gpower.html

(II) Via FTP:

(a) if you want the Macintosh-version of G*Power:

ftp://www.psychologie.uni-trier.de//pub/gpowermac/gpower212.sit.hqx (the program)

(b) if you want the MS-DOS-version of G*Power:

ftp://www.psychologie.uni-trier.de//pub/gpowerdos/gpower2d.exe
(German version)

ftp://www.psychologie.uni-trier.de//pub/gpowerdos/gpower2i.exe
(international version)

Set the file type to binary (omitting to set the file
type properly is a frequent

error!).

Convert the compressed file to a standard Macintosh or DOS file:

(a) Macintosh-version: Use StuffIt or the Stuffit Expander.
No additional

installation is necessary.

(b) DOS-version (self-extracting archive): GPower2i.exe
(international version)

or GPower2d.exe (German version). This will create a
subdirectory GPower in your

current working directory which will contain all necessary
files.

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(4) How to find help for using G*Power

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We have made available for you a www-based guide to G*Power at

http://www.psychologie.uni-trier.de:8000/projects/gpower/how_to_use_gpower.html

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(5) Address for correspondence

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Please report bugs and suggestions to improve the program to:

Axel Buchner

FB I - Psychologie

Universität Trier

D-54286 Trier

Germany

E-mail: buchner@cogpsy.uni-trier.de

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(6) Disclaimer

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We hereby disclaim all warranties relating to this software,
whether expressed or

implied, including without limitation any implied warranties
of merchantability

or fitness for a particular purpose. We will not be
liable for any special,

incidental, consequential, indirect or similar damages
due to loss of data or any

other reason, even if we or agents of ours have been
advised of the possibility

of such damages. In no event shall we be liable for
any damages, regardless of

the form of the claim. The person using the software
bears all risk as to the

quality and performance of the software.

*This page was created using TextToHTML. TextToHTML is a free software for Macintosh and is (c) 1995,1996 by Kris Coppieters*