I'm used to thinking about meta-analyses in terms of evaluating the impact of an IV on an outcome of interest (ex: relationship between a teacher's level of self-confidence and student outcomes), and I'm used to calculating r (or using t-test, F or p-values, etc to calculate g or d and then converting that to r).
However, for my current study I'm interested in first describing the prevalence of a particular attitude; specifically, to what extent do professionals (physicians, police, clergy, etc) hold stigmatizing views of the eldery? However, I'm not initially trying to compare across groups, and many studies only have one type of participant (e.g., all physicians). I've found a bunch of studies that essentially gave a measure of stigma to a set of participants and reported either:
a) The number or percent who responded with stigmatizing views or
b) The average and standard deviation stigma score (on a continuous scale) for the sample.
Is it possible to convert this data into an effect size? I've found many effect size calculators, but none that seem to deal with converting the prevalence of a trait from a single group into an effect size. I've seen several references to "proportion, prevalence, or central tendency effect sizes" but no formulas.
Any advice on extracting information from these papers and converting it to d, g, or r (or even an odds ratio) would be greatly appreciated!
Best Answer
Following Sutton et al. (2000: 18f), I would suggest converting proportions $p$ to logits:
$logit = log(odds) = log(\frac{p}{1-p}).$
Using the number of cases with an event ($N_{event}$) and without an event ($N_{\neg event}$), the variance of $logit$ is given by
$Var(logit) = \frac{1}{N_{event}} + \frac{1}{N_{\neg event}}$.
Reference
Sutton, A. J., K. R. Abrams, M. Jonas, T. A. Sheldon und F. Song, 2000a: Methods for meta-analysis in medical research. Wiley series in probability and mathematical statistics, Chichester; New York: Wiley.