I know nothing about the biological background here, but I also wonder if the standard meta-analytic approach is meaningful here. I also see some confusion in terminology (these are not "count data"!).
There appear to be only 3 observations per group in each of the studies -- the standard deviations in each of the studies are consequently very inaccurate estimates. A potential solution may be pooling SDs across studies. While I do not know what was measured in each of the "studies", I suspect that it may have been "the same thing". Therefore, I would suggest that the outcome should be the raw/unstandardized mean difference (i.e., ControlMean - TreatedMean) and not the standardized one (i.e., (ControlMean - TreatedMean) / SD). And Jim's comment is also spot-on -- does it make sense to compare those zeros with non-zeros? Best, Wolfgang > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > On Behalf Of Jim Lemon > Sent: Sunday, July 10, 2011 01:21 > To: Rosana Ferrero > Cc: r-help@r-project.org > Subject: Re: [R] Meta-analysis with zero values for mean and sd > > On 07/09/2011 08:16 PM, Rosana Ferrero wrote: > > Hi! > > I want to do a meta-analysis with count data for treatement/control > cases. > > Mi problem is that I need to use zero values (an informative value) for > the > > mean and standard deviation for one of the treatement, but R has a > > problem: "Studies > > with zero values for sd.e or sd.c get no weight in meta-analysis". I can > > agroup the case by Family (byvar=Family). > > Hi Rosana, > Your data indicates that in three studies, whatever was being measured > had a value of zero for each of the three spaghetti worms in the > treatment group. Maybe they were dead or something. You may be able to > get away with substituting a very small value (0.1 or something) for the > SD in these cases. However, I would look very carefully at what this > means. If, say, the worms are dead, is the measurement between live and > dead worms meaningful? Just a guess. > > Jim > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
