Include a Few Least Competent Users in Every Testing Sample

We have found that we learn an extraordinary amount by including one or more least competent users (LCUs) among participants, even if they do not make up a significant percentage of the eventual end users. An LCU is defined as an end user who represents the least skilled person who could potentially use

your product. In the example of the user profile for the chemical engineeringmarket, the LCU is a person with no computer experience, who has never used even a word processor, who is a high-school graduate, and so on. The LCU need not fall at the bottom of all the scales, but the LCU should be at the bottom of the majority of them. Why include LCUs even if the user profile is projected at mostly expert users? Simply this: If your least expert group can successfully use the product, if the]/ can muddle their way through the usability test, then you can assume that most other groups will also be able to use the product.

Of course, there are exceptions to every rule, but by and large, we have found the LCUs to be excellent indicators of a product's overall ease of learning. On the other hand, if the LCUs cannot get through the test, that is not necessarily an indictment. It does, however, reveal clues on how to fix fundamental problems of intuitiveness, orientation, or organization through redesign, more or better information in the instructions, and so forth. In addition, during early product development and exploratory tests, you learn much about the end

user's mental models through the eyes of the LCU, before the LCU has been