Are users more diverse than designs?

Twenty-five years ago, Dennis Egan published a review on the impact of individual differences in human-computer interaction, where he claimed that users are more diverse than designs are [5]. While being cited frequently, this claim has not been tested since then. An efficient research design for separating and comparing variance components is presented, together with a statistical model to test Egan’s claim. The results of a pilot study indicate that Egan’s claim does not universally hold. An extension to the claim is suggested, capturing the trade-offs when prioritizing user tasks. An alternative strategy towards universal design is proposed.