  Past research relates design creativity to 'divergent thinking,' i.e., how
well the concept space is explored during the early phase of design.
Researchers have argued that generating several concepts would increase the
chances of producing better design solutions. 'Variety' is one of the
parameters by which one can quantify the breadth of a concept space explored by
the designers. It is useful to assess variety at the conceptual design stage
because, at this stage, designers have the freedom to explore different
solution principles so as to satisfy a design problem with substantially novel
concepts. This article elaborates on and critically examines the existing
variety metrics from the engineering design literature, discussing their
limitations. A new distance-based variety metric is proposed, along with a
prescriptive framework to support the assessment process. This framework uses
the SAPPhIRE model of causality as a knowledge representation scheme to measure
the real-valued distance between two design concepts. The proposed framework is
implemented in a software tool called 'VariAnT.' Furthermore, the tool's
application is demonstrated through an illustrative example.
