The process here described is quite straightforward in concept, although highly complex mathematically. It is not the purpose of this paper to discuss in detail the technicalities, and it will be sufficient to remark that the factor Analysis used in MASA uses the FA6 programme of Cybernetic Research Consultants Ltd., providing oblique factors . An addition to the programme has been written by C.R.C., allowing for the calculation of variable shifts by calculating differences for occasional two and occasional three from a normalised score. Factor movements are calculated by summing the individuals' scores, each weighted by the regression weight of the variable in the factor. The method described provides precise, statistically valid, measurements of attitude change caused by an advertisement.