[R-meta] Issues when using rma.mv

[Diego Gallego García]

Good morning,

First post here, so I apologize if I do not explain my issue in the
best way.

I am currently conducting a review on the length of the dependence period
(time that the nestling spends with parents) in birds. I want to test which
ecological factors affect this variable.

My raw dataset has one row per species and per study (i.e., there are some
studies which account for more than one species, so I separate each species
studied in each research), with its corresponding variables of the
dependence period (PD: days), SD, N (number of individuals studied), etc...
My raw dataset should look like this (dummy data):

Study_ID       Species      Latitude     Body weight      Status
          DP        N        SD
1                    A                       50                3.4
      Resident              45          3        1.81
2                    A                       38                3.4
      Migrant                32          1         N/A
2                    B                        43               2.1
      Migrant                33         11       3.45
3                    B                        38               2.1
      Resident               38          6        2.45
3                    C                        12               3.6
     Resident               159        2         0

Now, as you may see, there are some studies with an n=1 (only one
individual was examined), so there is no valid SD for the study (i.e.,
N/A). Thus, for the escalc() formula, I should delete them. But what about
the last example? There were two individuals studied in that paper, and
both yielded the same result, so the SD is roughly 0.

Afterwards, when using rma.mv for a mixed-effects model, those studies with
SD=0 (then vi=0) are giving me problems. Specifically, there are some
warnings in my models:

Warning messages:
1: There are outcomes with non-positive sampling variances.
2: 'V' appears to be not positive definite.

The model is the following:
p1 <- rma.mv(data$yi, data$vi, mods= ~Latitude*Status,
               random=~1|Species, data=data)

Should I be worried about these warnings? Any way to fix them?

I appreciate any help.
Best,
*MSc Diego Gallego García*

Proyecto Águila del Chaco - Chaco Eagle Project
Center for the Study and Conservation of Raptors in Argentina *(CECARA)*
Institute of Earth and Environmental Sciences of La Pampa *(INCITAP)*
National Scientific and Technical Research Council *(CONICET)*

<https://www.instagram.com/proyectoaguilachaco/>

diegothen using gmail.com
https://www.researchgate.net/profile/Diego_Gallego_Garcia

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