Virtually all of the scale development approaches discussed in thisbook assume that the items making up a scale are unidimensional. Fac-tor analysis is the tool of choice for identifying which potential candi-date items will fit this assumption. Though the entire set of items inwhich a researcher is interested may be multidimensional, if he or shecan identify subsets that are unidimensional, then each of those subsetscan be treated as a separate scale and the work of developing ameasurement instrument (or perhaps more accurately, a set of relatedmeasurement instruments) can continue.