A Bluffer’s Guide to Meta-Analysis1 By Dr. Andy Field University of Sussex
What Is The Point of a Meta-Analysis? Psychologists are typically interested in finding general answers to questions. For example, Lotze et al (2001) did a study to see what areas of the brain were activated during anal stimulation: they inserted balloons (not party ones) into people’s rectums and inflated them while the person was in an fMRI scanner. Then they sang happy birthday and … OK, they didn’t, but they really did do the balloon thing. One of the areas of the brain in which they were interested was the secondary somatosensory cortex (S2). Lotze et al. were probably interested in what brain regions were activated in their sample as a means of extrapolating to a wider population. However, what typically happens in science, is some other people then come along, they think ‘hmm, shoving balloons up people’s arses looks like a fun way to spend some research money’ and off they go with their fMRI scanner and balloons to traumatise the local college populous. Of course, sooner or latter many more researchers will realise that this whole bum balloon thing is much more fun than whatever it is they’re supposed to be doing, and before you know it, the literature is riddled with research papers (and the world is riddled with people who have conditioned surprised expressions on their face whenever they see an fMRI scanner). Can we assimilate all of these studies to improve the accuracy of our conclusions about which brain areas are activated by having crazy psychologists inflate balloons up our back passages? Until about 30 years ago, the answer was simply to do a subjective evaluation of the literature. A typical review would entail the author collating articles on the give