Dear all, I have a question regarding the rma.mv function. Some QM tests (test of moderation) are not significant. However, I continued to investigate both levels of the moderator regardless by removing the intercept (i.e with placing a -1 at the end) How sensible is this and what kind of conclusions can I draw when both levels (after removing the intercept) produce significant results. I understand I can?t draw any overall conclusions for the a priori hypotheses, considering the test of moderation was not significant - but generally, I wonder, whether it is ?ok? to report this - or whether it is simply wrong to continue with any analysis if the QM test is not significant. Many thanks for clarifying. Kind regards, Tina Dudenh?ffer
[R-meta] Removing the intercept in rma.mv after non-significant QM/F test
4 messages · Michael Dewey, Wolfgang Viechtbauer, T D
Dear Tina When you leave the intercept in you are testing whether the two levels differ. When you take it out you are separately testing for each whether its coefficient differs from zero. Those are clearly not the same. Michel
On 09/12/2021 12:32, T D wrote:
Dear all, I have a question regarding the rma.mv function. Some QM tests (test of moderation) are not significant. However, I continued to investigate both levels of the moderator regardless by removing the intercept (i.e with placing a -1 at the end) How sensible is this and what kind of conclusions can I draw when both levels (after removing the intercept) produce significant results. I understand I can?t draw any overall conclusions for the a priori hypotheses, considering the test of moderation was not significant - but generally, I wonder, whether it is ?ok? to report this - or whether it is simply wrong to continue with any analysis if the QM test is not significant. Many thanks for clarifying. Kind regards, Tina Dudenh?ffer
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Indeed! @Tina: Also see this write-up: https://www.metafor-project.org/doku.php/tips:models_with_or_without_intercept Best, Wolfgang
-----Original Message----- From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-project.org] On Behalf Of Michael Dewey Sent: Thursday, 09 December, 2021 16:59 To: T D; r-sig-meta-analysis at r-project.org Subject: Re: [R-meta] Removing the intercept in rma.mv after non-significant QM/F test Dear Tina When you leave the intercept in you are testing whether the two levels differ. When you take it out you are separately testing for each whether its coefficient differs from zero. Those are clearly not the same. Michel On 09/12/2021 12:32, T D wrote:
Dear all, I have a question regarding the rma.mv function. Some QM tests (test of moderation) are not significant. However, I continued to
investigate both levels of the moderator regardless by removing the intercept (i.e with placing a -1 at the end)
How sensible is this and what kind of conclusions can I draw when both levels
(after removing the intercept) produce significant results. I understand I can?t draw any overall conclusions for the a priori hypotheses, considering the test of moderation was not significant - but generally, I wonder, whether it is ?ok? to report this - or whether it is simply wrong to continue with any analysis if the QM test is not significant.
Many thanks for clarifying. Kind regards, Tina Dudenh?ffer
Hi Michael, Yes, that?s clear - I was rather wondering how to report this but Wolfgang forwarded a link. All clear now. Many thanks, Tina
On 9 Dec 2021, at 16:59, Michael Dewey <lists at dewey.myzen.co.uk> wrote: Dear Tina When you leave the intercept in you are testing whether the two levels differ. When you take it out you are separately testing for each whether its coefficient differs from zero. Those are clearly not the same. Michel On 09/12/2021 12:32, T D wrote:
Dear all, I have a question regarding the rma.mv function. Some QM tests (test of moderation) are not significant. However, I continued to investigate both levels of the moderator regardless by removing the intercept (i.e with placing a -1 at the end) How sensible is this and what kind of conclusions can I draw when both levels (after removing the intercept) produce significant results. I understand I can?t draw any overall conclusions for the a priori hypotheses, considering the test of moderation was not significant - but generally, I wonder, whether it is ?ok? to report this - or whether it is simply wrong to continue with any analysis if the QM test is not significant. Many thanks for clarifying. Kind regards, Tina Dudenh?ffer
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