[R-meta] How to conduct a meta-analysis on multiple-treatment studies with a repeated measure designs?

[Koenraad van Meerbeek]

Dear all,

We want to do a meta-analysis with the metafor package in R to study the effect of multiple experimental treatments on species diversity over time. First of all, we use data from multiple-treatment studies, in which the effect of different treatments are compared against a single control group. So far, this is the same as the Gleser & Olkin (2009) example on the metafor website. However, some of the studies also measured the effects of the treatments over time (repeated measures design).

This is an example of how our data looks like (simplified). We also want to include magnitude of the treatment and duration of the study as moderator variables.

Study

Treatment

Year

Species diversity

Magnitude

Duration

1

Control

1

1.35

0

1

1

TR1

1

0.78

0.75

1

1

TR2

1

0.23

1.50

1

1

Control

2

...

...

2

1

TR1

2





2

1

TR2

2





2

2

Control

1





1

2

TRa

1





1

2

TR2b

1





1

2

Control

2





2

2

TRa

2





2

2

TR2b

2





2


We started to calculate the log response ratio:
dat <- escalc(measure = "ROM", n1i = dat$n1i, n2i = dat$n2i, m1i = dat$m1i,  m2 = dat$m2i, sd1i = dat$sd1i, sd2i = dat$sd2i)

And then fitted following mixed effects model:
res.mv <- rma.mv(yi, vi, mods = ~ Magnitude + Duration, random = ~ Study| ID, data=dat)

We did not yet try to calculate a variance-covariance matrix as the Gleser & Olkin (2009) example, because we did not know how to take the repeated measures design into account.

How do you suggest to proceed? Expand the res.mv with a variance-covariance matrix? How would you do that? Or aggregate the data (across years) in some way and then follow the Gleser & Olkin (2009) example?

Best,

-----
Koenraad Van Meerbeek
Postdoctoral researcher
Center for Biodiversity Dynamics in a changing world (BIOCHANGE)
Section for Ecoinformatics & Biodiversity
Department of Bioscience | Aarhus University
Ny Munkegade 114, 8000 Aarhus C, Denmark
E-mail: koenraad.vanmeerbeek[at]bios.au.dk
Mobile: +32 479 206957


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