Accounting for Homogeneity Assumption

Virzi’s homogeneity assumption in usability test definitely addresses the problem of cost-benefit ratio and at the same time makes a case for small-sized companies to invest in usability-testing. However, as exemplified by Lewis modification of the binomial model, the homogeneity breaks down when the test is concerned with sub groups. K &K earlier noted that there is a need for a “varied user […] in cases where the system is designed for organizations and not for individuals” (K&K 2); how does then Virzi’s assumption hold true in case of organizational set-up. If there is a need to identify unique problems we would need distinct heterogeneous groups (Caulton 5), which in turn challenges the homogeneity assumption in terms of decreased power. How then we could resolve the problem of decreased p with increased number of heterogeneous subgroups which account for higher proportions of unique problems? I think one way to do it is to identify the representative sub-groups from the possible distinct groups. But, how do we account for these representative sub-groups from the heterogeneous sample size?

Also, I think that Vatrapu’s concern of addressing cross-cultural imperative in structured-interview can be related to the homogeneity assumption. In my view, culture as an independent variable plays an important role in indentifying unique problems. Therefore, I think the question of unique problems would not depend on increased number of heterogenous subjects as far as the cultural impediment exists. On the other hand, there the homogenous assumption would hold good for indentifying shared problems even if there is a manifest difference between the interviewer and the subjects. Thus, when designing interface for international audience is it still possible to identify unique problems within the homogenous group if the cultural barrier is removed.