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From |
"Trelle Sven" <strelle@ctu.unibe.ch> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: Discrepancy between metan vs metareg with one variable |

Date |
Wed, 19 Dec 2012 11:55:28 +0100 |

If my understanding is correct I would assume that this is because a meta-regression estimates one random-effect (between-trial heterogeneity; one tau-square==variance of the underlying normal distribution) whereas a sub-group analysis using metan estimates separate random-effects for each subgroup (n tau-squares). Hence,interpretation is different for these two approaches. You will see large differences between the two approaches if the stratification is able to explain heterogeneity only in some subgroups but not all. To replicate the test-statistic you would need to force metan to estimate only one tau-square (across the subgroups) but I wouldn't know how to do this. Best Sven TRelle -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Paul Karner Sent: Dienstag, 18. Dezember 2012 18:09 To: statalist@hsphsun2.harvard.edu Subject: Re: st: Discrepancy between metan vs metareg with one variable Thanks for your reply. They can be quite different -- in one instance by more than 10%. I've played around with the different options for specifying the method of variance estimation and that does not resolve the large discrepancy. Potentially related, I notice when calculating the test statistic for the difference between effect sizes for two subgroups that the z-stat from the meta regression is much smaller than the hand-calculated z-stat I get [using the pooled standard error estimate sqrt(se_group1^2 + se_group0^2)]. This is only true for random-effects meta regression (i.e. the hand-calculated z-stat is identical to that reported by "vwls"). Is this because the pooled standard error on which coefficient test statistics are based in random effects meta regression somehow also account for between-study heterogeneity? If so, does anyone know exactly how one would replicate the z-stats reported by metareg, z by hand? Thank you again for your insight! Paul On Tue, Dec 18, 2012 at 10:09 AM, JVerkuilen (Gmail) <jvverkuilen@gmail.com> wrote: > On Tue, Dec 18, 2012 at 9:30 AM, Paul Karner <pkarner@gmail.com> wrote: >> I have a question about Stata's (user-written) meta analysis functions. >> >> When I run metareg with a single variable ("group1"), why is the >> coefficient estimate on group1 slightly different from what I get >> when I run metan, random, by(group1) and subtract the effect >> estimates for the two subgroups (i.e., group1==1 and group1==0)? > > How different is different? The two methods may be using slightly > different estimators as defaults, so for instance if one is using Der > Simonian-Laird and the other REML, you're going to have differences. > You need to check to see if you're estimating the model the same way > and then compare. Even then they may well not line up perfectly if > there are other slight differences in the programming between the two > procedures, but they should be on par up to about four decimal places. > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Discrepancy between metan vs metareg with one variable***From:*Paul Karner <pkarner@gmail.com>

**Re: st: Discrepancy between metan vs metareg with one variable***From:*"JVerkuilen (Gmail)" <jvverkuilen@gmail.com>

**Re: st: Discrepancy between metan vs metareg with one variable***From:*Paul Karner <pkarner@gmail.com>

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