Factor Analysis is commonly used to reveal the structure underlying the multiple attributes that describe marketing stimuli. This paper provides a theoretical investigation and an empirical comparison of two approaches to Factor Analysis that are based on two different sources of variation in the input data. The “Among” Analysis is based on variation across marketing stimuli, while the “Within” Analysis is based on variation across individuals responding to the same marketing stimulus. We identify conditions under which one approach is superior to the other. If both approaches are applicable, we recommend the use of the “Total” analysis that pools the variation across stimuli and individuals. An empirical study, in the context of consumers’ cognitive response to ads, shows that the Among Analysis results can be seriously distorted by differential familiarity with the ads so that it is important to partial out the spurious effects of familiarity.