[R-meta] Direction of the effect sizes

Miguel García Kml migueline at gmail.com
Wed Dec 6 18:57:09 CET 2017

Dear Michael:

Thank you very much for your help. What I did was to do the meta-analysis
by groups to avoid this problem, but due to my inexperience I wanted to be
sure that it was correct and my question made sense.

However, I still worry about the sign, especially in the meta-regression
since, for example, longer exposure times will produce larger effects (both
positive and negative, depending on the music and task), and if I do not
use the absolute values the effects will be canceled, implying something
that is not correct. Does this reasoning make any sense?


2017-12-05 14:16 GMT+01:00 Michael Dewey <lists at dewey.myzen.co.uk>:

> Dear Miguel
> I think the answer is going to depend on exactly what analysis you are
> doing. If you analyse the studies in several separate m-a then I do not see
> any problem as the differences come out in the interpretation. If you are
> going to do a multi-level m-a with both outcomes and both interventions
> included then the problem will be taken care of by the effect of the
> moderators and possibly their interaction.
> I can see that things may in some cases be made easier by reflecting the
> effect sizes (multiplying by -1) for some groups of studies but I find it
> hard to think of a problem which would be solved by using absolute values.
> I suppose if you were trying to detect a form of bias which meant that too
> few studies near the null were available it might be necessary.
> Michael
> On 05/12/2017 10:32, Miguel García Kml wrote:
>> 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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> --
> Michael
> http://www.dewey.myzen.co.uk/home.html

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