RE: Sample size

[morphmet]

-------- Original Message --------
Subject:        RE: Sample size
Date:   Fri, 13 Nov 2009 04:34:31 -0800 (PST)
From:   Samuel Okoye <samu...@yahoo.com>
To:     morphmet@morphometrics.org



Thank you very much for your reply.

If it is not required to have equal sample sizes (n1=n2), is there any
rule of thump how big the difference between the two group (e.g. n1=5
n2=15)? Does this also apply for multivariate data?

Many thaks in advance,
Samuel

--- On *Thu, 11/12/09, morphmet
/<morphmet_modera...@morphometrics.org>/* wrote:


    From: morphmet <morphmet_modera...@morphometrics.org>
    Subject: RE: Sample size
    To: "morphmet" <morphmet@morphometrics.org>
    Date: Thursday, November 12, 2009, 10:58 AM



    -------- 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
    </mc/compose?to=ro...@life.bio.sunysb.edu>>
    Organization: Ecology & Evolution
    To: <morphmet@morphometrics.org
    </mc/compose?to=morph...@morphometrics.org>>
    References: <4af5219d.1070...@morphometrics.org
    </mc/compose?to=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
    </mc/compose?to=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
    </mc/compose?to=samu...@yahoo.com>>
     > To:     morphmet_modera...@morphometrics.org
    </mc/compose?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
     >
     >
     >
     > --
     > Replies will be sent to the list.
     > For more information visit http://www.morphometrics.org



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