[R-meta] meta-analysis of response ratios with low sample sizes
Dear Wolfgang (and users of the meta-analysis mailing list), I am currently conducting a meta-analisis where I want to assess body size shifts in vertebrates living in islands compared to mainland populations (a.k.a the island rule). I am using response ratios between the mean size of the island population and the mean size of the mainland population. In some cases I have measurements for only 2 specimens, and I calculate mean and SD for those 2 specimens in order to calculate the sampling variance. However, many people would argue that calculating the SD of 2 data points is a bit meaningless in most contexts, but in a meta-analytical context I would expect that response ratios based on N = 2 for either the treatment or control, or both, would be downweighted in the metaanalysis and thus it is both informative and interesting to include them in the analyses. I would like to know if other people have encountered these situations and how they dealt with it. Also, what?s your opinion, Wolfgang? I have a second query, in this same analysis I have cases where only one specimen is measured, and thus the SD is zero. To be able to calculate the sampling variance I add a small constant (0.5) to both the numerator and denominator of the formula. Is this a sensible way to proceed or shall I just discard cases where only 1 specimen is measured in either of the two populations (or both of them)? Thanks a lot for your time, I am looking forward to your thoughts on these two queries. Best, Ana
Ana Ben?tez L?pez Department of Environmental Science Faculty of Science, Radboud University Heyendaalseweg 135, Huygens building; 2nd floor, wing 6; room 02.611 PO Box 9010 | 6525 AJ | Nijmegen T: +31 (0)24 3653291 | E: a.benitez at science.ru.nl www.ru.nl/environmentalscience/ https://www.researchgate.net/profile/Ana_Benitez-Lopez orcid.org/0000-0002-6432-1837 http://www.environmentalevidencejournal.org/ [[alternative HTML version deleted]]