[R-meta] Direction of the effect sizes

Michael Dewey lists at dewey.myzen.co.uk
Thu Dec 7 13:24:01 CET 2017

Dear Miguel

Can you show us an example of the model you are proposing? I think that 
with a careful choice of moderators the problem may be solvable.

On 06/12/2017 17:57, Miguel García Kml wrote:
> 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?
> Miguel
> 2017-12-05 14:16 GMT+01:00 Michael Dewey <lists at dewey.myzen.co.uk 
> <mailto: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
>                  [[alternative HTML version deleted]]
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>     -- 
>     Michael
>     http://www.dewey.myzen.co.uk/home.html
>     <http://www.dewey.myzen.co.uk/home.html>


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