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[R-meta] Question on effect sizes

Hi,

a couple of ideas that may be obvious to you but the provided 
description is rather short, so I don't know whether you have thought 
about the following points:

1. Did you try to contact the authors of the studies? Maybe they will be 
willing to provide the missing statistics or the data set. The 
willingness varies obviously between researchers (and research areas) 
but it is often worth the effort.

One could contact the corresponding author and ask for the statistics or 
the data set (providing the choice can increase the success rate). If 
you don't receive an answer within several days (e.g. one week) thwn one 
can try to contact the other authors. Recently I used this strategy for 
two different meta-analyses and approximately 80% - 90% of the research 
teams wrote back. Obviously, not all of them could provide answers or 
data (hard drive failure etc.) but approximately 30% - 50% of the 
authors provided additional information.

2. If you have already explored the first strategy and the relevant 
information is still missing, then one could try to reconstruct it. It 
is something that you were referring to but the description is rather 
short, so I cannot infer what is meant by pooled SD etc.
One could try to rearrange the formulas to compute the missing 
information manually but if there are two unknowns (e.g. SD and M for 
one group is missing) then it is not possible.
Nevertheless, one could try to make some guesstimates (e.g. are the SDs 
for both groups in other studies similar? if yes than one could make a 
respective guesstimate for the missing information) in order to impute 
the data.
One could even make several guesstimates and test these different 
scenarios to test the robustness of the findings. Another sensitivity 
analysis would be to compare meta-analytic results based on studies with 
without missing information and the scenarios with guesstimates.

3. It is probably obvious to you but dropping the studies with missing 
information is also a possibility. However, it could bias the results 
(if the dropped studies differ significantly from the included studies).


Hope it helps!

Best wishes,