[R-meta] R-sig-meta-analysis Digest, Vol 24, Issue 11

Rushkin, Megan C Meg@n@C@Ru@hk|n @end|ng |rom kpchr@org
Tue May 14 18:06:31 CEST 2019

Thank you both for your very thoughtful answers! I greatly appreciate your explanations and resources, and it's helpful to know that both methods are valid ways of addressing I^2.  

Thanks again,

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Subject: R-sig-meta-analysis Digest, Vol 24, Issue 11

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Today's Topics:

   1. Re:  Confidence intervals for effect sizes in pretest
      posttest control group designs (=?UTF-8?Q?C=C3=A9lia_Sofia_Moreira?=)
   2. Re: Differences in I^2 estimation between meta and metafor
      packages (Guido Schwarzer)


Message: 1
Date: Mon, 13 May 2019 21:52:59 +0100
From: =?UTF-8?Q?C=C3=A9lia_Sofia_Moreira?=
	<celiasofiamoreira using gmail.com>
To: "Viechtbauer, Wolfgang (SP)"
	<wolfgang.viechtbauer using maastrichtuniversity.nl>
Cc: "r-sig-meta-analysis using r-project.org"
	<r-sig-meta-analysis using r-project.org>
Subject: Re: [R-meta]  Confidence intervals for effect sizes in
	pretest posttest control group designs
	<CAJhU6eEbh_jvLFrgvjy-6pVHO4bFgTVMrAAQ809MXbx5F6=0ZQ using mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Dear Professor Wolfgang Viechtbauer,

Thank you so much for your great support!
I was expecting the answer to be something complicated because I took a look at your paper (but I didn't have the time to examine it):
Viechtbauer, W. (2007). Approximate confidence intervals for standardized effect sizes in the two-independent and two-dependent samples design. *Journal of Educational and Behavioral Statistics, 32*(1), 39–60.

I admire that even when you answer this too basic questions (too basic for you), you answer in an elegant way.
Science needs people like you! Thanks.

Kind regards,

Viechtbauer, Wolfgang (SP) <wolfgang.viechtbauer using maastrichtuniversity.nl>
escreveu no dia segunda, 13/05/2019 à(s) 09:49:

> Hi Célia,
> An approximate 95% CI can be obtained with:
> dat$yi + c(-1,1) * qnorm(.975) * sqrt(dat$vi)
> Best,
> Wolfgang
> -----Original Message-----
> From: R-sig-meta-analysis [mailto:
> r-sig-meta-analysis-bounces using r-project.org] On Behalf Of Célia Sofia 
> Moreira
> Sent: Sunday, 12 May, 2019 23:18
> To: r-sig-meta-analysis using r-project.org
> Subject: [R-meta] Confidence intervals for effect sizes in pretest 
> posttest control group designs
> Dear all,
> I would like to compute 95% confidence intervals for the effect sizes 
> in a pretest posttest control group design, such as the "Morris example"
> presented in:
> http://www.metafor-project.org/doku.php/analyses:morris2008
> Can you please tell me how to do this?
> Kind regards,

	[[alternative HTML version deleted]]


Message: 2
Date: Tue, 14 May 2019 11:59:20 +0200
From: Guido Schwarzer <sc using imbi.uni-freiburg.de>
To: "Viechtbauer, Wolfgang (SP)"
	<wolfgang.viechtbauer using maastrichtuniversity.nl>, "Rushkin, Megan C"
	<Megan.C.Rushkin using kpchr.org>, "r-sig-meta-analysis using r-project.org"
	<r-sig-meta-analysis using r-project.org>
Subject: Re: [R-meta] Differences in I^2 estimation between meta and
	metafor packages
	<da867550-f7a4-b8db-0c96-e5833ad5c5bc using imbi.uni-freiburg.de>
Content-Type: text/plain; charset="utf-8"; Format="flowed"

Am 13.05.19 um 10:45 schrieb Viechtbauer, Wolfgang (SP):

> Hi Megan,
> This is answered here:
> http://www.metafor-project.org/doku.php/faq#how_are_i_2_and_h_2_comput
> ed_i

This website nicely describes the differences in the calculation of I2 in metafor and meta. As this is written from the metafor perspective, I would like to describe why meta uses the "other" definition. ;-)

Wolfgang mentions two advantages of the metafor implementation of I2:
1) "more general definition"
2) "values of I2 and H2 will be consistent with ... tau2"

I agree that the metafor implementation is more general as one gets a different I2 value for each estimation method of tau2. However, the meta implementation is also based on a generalization (to the situation in which precisions differ between studies) - see section 3.3 in Higgins & Thompons (2002).

On the other hand, while the metafor implementation guarantees consistent estimates for I2 and tau2, the meta implementation guarantees consistency of the I2 estimate and the test for heterogeneity (which - like I2 - is based on Q and the number of studies).

In summary, one should know the differences in the estimation of I2 between metafor and meta, however, there is (in my opinion) no clear "winner".

Best wishes, Guido


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