[R-meta] potential shortcomings of combining meta-analysis

[James Pustejovsky]

Hi Diego,

The log response ratio is a scale-free metric, so linear transformations of
the units of measurement will not change the value of lnRR. From what you
have described, it seems that u1 is a linear transformation of u2 (u1 = 100
* u2), and so in principle lnRR measures calculated from measurements on
either scale should be directly comparable.

James

On Thu, Dec 10, 2020 at 4:15 PM Diego Grados Bedoya <diegogradosb using gmail.com>
wrote:

> Dear all,
>
> I am struggling about the implications of combining two meta-analyses (the
> potential shortcomings of conducting a second-order meta-analysis):
>
> Meta-analysis1 was achieved with the ln(RR1)[based on variable x1]
>
> Meta-analysis2 was achieved with the ln(RR2) [based on variable X2]
>
> There is an underlying relation between the units of X1 (u1) and X2 (u2):
>
> u3=u1*3k ; u3=u2*300k
>
> I wonder if it is possible to perform such analysis just including for
> instance as a moderator the categorical variable for units (units1,units2)?
> Am I missing something in the implications of the units that would affect
> the correct comparison of ln(RR1) and ln (RR2)? I have consulted the work
> of Schmidt and Oh (2013), Castellanos and Verdú (2012), Tamin (2011), and
> other articles related to effects sizes calculations but I am not pretty
> sure if I am not considering some kind of previous correction of the effect
> sizes of the first order meta-analyses (or if it is not possible at all).
>
> Maybe you can point me out in some direction about it.
>
> Thank you in advance,
>
> Diego
>
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