[R-meta] rma.mv only for better SEs

[Viechtbauer, Wolfgang (SP)]

This is not correct. Also ordinary multilevel models have a weight matrix.

>-----Original Message-----
>From: Simon Harmel [mailto:sim.harmel using gmail.com]
>Sent: Monday, 31 January, 2022 21:14
>To: Viechtbauer, Wolfgang (SP)
>Cc: R meta
>Subject: Re: [R-meta] rma.mv only for better SEs
>
>This is very helpful, thank you so very much.
>
>Simon
>ps. This may be loosely relevant but in ordinary multilevel models, we don't use
>weights, but still random-effects' structures do have a bearing on the fixed
>effect estimates. So, aside from weights, something else from random-effects must
>have an impact on fixed-effect magnitude.
>
>On Mon, Jan 31, 2022 at 2:04 PM Viechtbauer, Wolfgang (SP)
><wolfgang.viechtbauer using maastrichtuniversity.nl> wrote:
>Right, sorry, that was a typo.
>
>Best,
>Wolfgang
>
>>-----Original Message-----
>>From: Simon Harmel [mailto:sim.harmel using gmail.com]
>>Sent: Monday, 31 January, 2022 19:29
>>To: Viechtbauer, Wolfgang (SP)
>>Cc: R meta
>>Subject: Re: [R-meta] rma.mv only for better SEs
>>
>>Sure, but didn't you by any chance mean to say:
>>"The random effects structure determines the weight matrix, which in turn
>affects
>>the estimates of the **fixed effects**".
>>
>>On Mon, Jan 31, 2022 at 12:23 PM Viechtbauer, Wolfgang (SP)
>><wolfgang.viechtbauer using maastrichtuniversity.nl> wrote:
>>The random effects structure determines the weight matrix, which in turn affects
>>the estimates of the random effects.
>>
>>Best,
>>Wolfgang
>>
>>>-----Original Message-----
>>>From: Simon Harmel [mailto:sim.harmel using gmail.com]
>>>Sent: Monday, 31 January, 2022 18:29
>>>To: Viechtbauer, Wolfgang (SP)
>>>Cc: R meta
>>>Subject: Re: [R-meta] rma.mv only for better SEs
>>>
>>>I have done it, and in my case the results differ. But my point was, is my
>>>explanation regarding why they differ accurate?
>>>
>>>On Mon, Jan 31, 2022 at 11:24 AM Viechtbauer, Wolfgang (SP)
>>><wolfgang.viechtbauer using maastrichtuniversity.nl> wrote:
>>>Just try it out and you will see what happens.
>>>
>>>Best,
>>>Wolfgang
>>>
>>>>-----Original Message-----
>>>>From: Simon Harmel [mailto:sim.harmel using gmail.com]
>>>>Sent: Monday, 31 January, 2022 18:21
>>>>To: Viechtbauer, Wolfgang (SP)
>>>>Cc: R meta
>>>>Subject: Re: [R-meta] rma.mv only for better SEs
>>>>
>>>>Thank you, Wolfgang. I asked this, because I noticed applying RVE to an
>>rma.mv()
>>>>model has no bearing on the estimates of fixed effects themselves, and just
>>>>modifies their SEs.
>>>>
>>>>So, I wondered if the same rule, at least "in principle", should apply when we
>>>go
>>>>from rma() to rma.mv().
>>>>
>>>>But is there a principle regarding how random effects affect the fixed
>effects?
>>>>
>>>>For instance, in:
>>>>
>>>>1- rma.mv(y ~ 1, random = ~ 1|study/obs), the overall average only represents
>>>the
>>>>average of study-level effects.
>>>>
>>>>But, in:
>>>>
>>>>2- rma.mv(y ~ 1, random = ~ 1|study/outcome/obs), the overall average
>>represents
>>>>the average of study-level effects additionally affected by the outcome-level
>>>>effects within them.
>>>>
>>>>And thus, 1- and 2- may give different overall averages, right?
>>>>
>>>>Simon
>>>>
>>>>On Mon, Jan 31, 2022 at 11:00 AM Viechtbauer, Wolfgang (SP)
>>>><wolfgang.viechtbauer using maastrichtuniversity.nl> wrote:
>>>>Generally, two models with different random effects structures will also give
>>>you
>>>>different estimates of the fixed effects (unless the estimates of the
>>>>variance/covariance components happen to be such that the two models collapse
>>>>down to the same structure).
>>>>
>>>>Best,
>>>>Wolfgang
>>>>
>>>>>-----Original Message-----
>>>>>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org]
>>On
>>>>>Behalf Of Simon Harmel
>>>>>Sent: Monday, 31 January, 2022 17:49
>>>>>To: R meta
>>>>>Subject: [R-meta] rma.mv only for better SEs
>>>>>
>>>>>Hello List Members,
>>>>>
>>>>>Reviewing the archived posts, my understanding is that my studies can
>>>>>produce multiple effects, so I should use rma.mv() not rma().
>>>>>
>>>>>Also, I understand rma.mv() ensures that I get more accurate SEs for my
>>>>>fixed effects relative to rma().
>>>>>
>>>>>BUT does that also mean that, by definition, rma.mv() should have no
>>>>>bearing on the magnitude of the fixed effects themselves and only modifies
>>>>>their SEs relative to rma()?
>>>>>
>>>>>Thank you,
>>>>>Simon