RE: Sample size

[morphmet]

-------- Original Message --------
Subject: RE: Sample size
Date: Thu, 12 Nov 2009 10:39:35 -0800 (PST)
From: F. James Rohlf <ro...@life.bio.sunysb.edu>
Organization: Ecology & Evolution
To: <morphmet@morphometrics.org>
References: <4af5219d.1070...@morphometrics.org>

Do you mean for morphometric data (multivariate) or just univariate
data? For the univariate case you could check Section 9.8 in Biometry
for a method to estimate sample size. It does not, however, consider
the unequal sample size case.

In general, equal sample sizes are not required. The main advantage of
equal sample sizes is that they are more efficient. For a given total
sample size, n1+n2, you will have greater statistical power if n1=n2.
Having equal sample sizes also make the computations slightly simpler
but that is no longer much of an issue when computers are used to
perform all of the calculations.

=========================
F. James Rohlf
Distinguished Professor, Stony Brook University
http://life.bio.sunysb.edu/ee/rohlf

-----Original Message-----
From: morphmet [mailto:morphmet_modera...@morphometrics.org]
Sent: Saturday, November 07, 2009 2:28 AM
To: morphmet
Subject: Sample size



-------- Original Message --------
Subject:        Sample size
Date:   Wed, 4 Nov 2009 06:40:15 -0800 (PST)
From:   Samuel Okoye <samu...@yahoo.com>
To:     morphmet_modera...@morphometrics.org



Dear all,

I would be most grateful if you tell me how important to have
balanced
sample sizes for the t-test and ANOVA? Should the sample sizes
always be
equal? If not how big should the difference between them be? How
can I
do sample size calculaction for unbalanced t-test or ANOVA?

Many thanks in advance,
Samuel



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