You need a friendly statistician to help you out! Most Unis will have some kind of facility for getting staff/postgrads statistical advice, ask the postgrad office or maybe your supervisor?
Meta-analyses are complex, especially the literature search. If you want it to be publishable, then you will need to ensure that your search is as thorough as possible and that you have dealt with (or attempted to deal with!) such things as file-drawer bias/publication bias i.e. negative results tend not to be published and hence, if your search only reveals published studies (which tend to be positive) this can bias your results. Ways to check for unpublished studies are to search the Index of Theses and to contact researchers in the field to ask if they have unpublished work.