Meta-analysis is a statistical technique for amalgamating, summarising, and reviewing previous quantitative research. By using meta-analysis, a wide variety of questions can be investigated, as long as a reasonable body of primary research studies exist. Selected parts of the reported results of primary studies are entered into a database, and this "meta-data" is "meta-analyzed", in similar ways to working with other data – descriptively and then inferentially to test certain hypotheses.
Meta analysis can be used as a guide to answer the question 'does what we are doing make a difference to X?', even if 'X' has been measured using different instruments across a range of different people. Meta-analysis provides a systematic overview of quantitative research which has examined a particular question.
The appeal of meta analysis is that it in effect combines all the research on one topic into one large study with many participants. The danger is that in …