[R-meta] When to remove the intercept and other questions

Rafael Rios bior@f@elrm @ending from gm@il@com
Sat May 19 03:56:48 CEST 2018

Dear Dr. Wolfgang and All,

I have some doubts that you could help me to clarify. I read e-mails in
R-meta list of a conversation between Samuel Knapp and James Pustejovsky
with the title "Testing of moderators in rma()". James clarified the

"When the model includes an intercept term, the omnibus test does *not*
include the intercept. So the null hypothesis is b1 = 0 and b2 =0.

If you fit the model without the intercept, then the equivalent to the
omnibus test from the model with an intercept would be that the average
effect sizes are all equal, as in b1 = b2 = b3."

I want to compare the differences between effect sizes of four subgroups
from a categorical moderator. According James, I should remove the
intercept from the meta-analysis. I have had different results including or
removing the intercept. That is why I am insecure about to use this
approach. What do you think? Is it reasonable to remove the intercept in my

I also have some questions about how to obtain the intercept and slope from
multi-level meta-analysis with two moderators, a categorical moderator and
a continuous). How can I estimate the intercept and slope of each subgroup
to include the straights in a graph.

Every help is welcome!

Best wishes,

Rafael Rios Moura.
*scientia amabilis*

PhD in Ecology and Conservation
Postdoctoral Researcher
Universidade Estadual de Campinas (UNICAMP)
Campinas, São Paulo, Brazil
ORCID: http://orcid.org/0000-0002-7911-4734
Research Gate: https://www.researchgate.net/profile/Rafael_Rios_Moura2
Currículo Lattes:


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