[R-meta] Direction of the effect sizes

[Miguel García Kml]

Hello everyone!

A doubt has arisen that is perhaps quite basic/absurd, but which takes me
into my head for a while. I will try to explain my doubt in the simplest
way.

Imagine that we have two styles of music (let's say classical and rock) and
different psychological measures (scores in a memory task and levels of
anxiety). Suppose that classical music is tremendously relaxing and
therefore reduces anxiety levels, but it will worsen the results in memory
tasks. On the other hand, rock music will increase anxiety levels, but will
improve memorization. In this way, studies would display positive and
negative effect sizes in memory scores and anxiety, which indicates
effectiveness, no matter what the direction is (strange example, but it is
easier to understand that way).

Two doubts arise regarding this:

1) Should I use the absolute values of the effect size? since, although
some ES are negative, it indicates effectiveness as a whole (my
meta-analysis is about effectiveness). For instance, classical music
exposure might display relaxing effects (+ES) that are incompatible with
memorization (-ES), but as a whole, it shows effectiveness regardless of
the direction of the effect size.

2) If I should use the absolute values, should I use them in all the
analyzes? (i.e., meta-regression, funnel plot, influence diagnosis, etc.)
Or perhaps just in the regression analysis to be able to explain the
heterogeneity in terms of effectiveness? I am confused.

I hope that I have explained my question correctly, and I apologize if it's
too obvious. Thank you very much!

Best,

Miguel

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