Someone noted that the usual meta analysis is carried out for the study on two treatment groups, usually for a difference in means. What if you had several studies estimating not a difference in means, but just estimates of a single mean. Could you conduct a meta-analysis in this situation?
Yes, you can do this. The statistics change slightly, but in a predictable and logical way. The general concept and the general procedures stay the same.
It gets a bit trickier when the statistic of interest is a single proportion (e.g., sensitivity/specificity), especially when there are some publications where the proportion equals 1.0. If you try to weight by the inverse variance, these studies get infinite weight.