Diagnostic testing: definition & origins

By |2018-12-28T10:36:43+00:00November 23rd, 2018|

What is Diagnostic Testing?

Diagnostic testing is a method for finding faults in information designs. We call it diagnostic because it follows the same logic used by doctors to discover, treat, and cure patients.

Like doctors, we as communication and information designers look for symptoms of disease. But in this case the disease is not in people, but in public documents that people cannot use. In information design, the sick patient is the document. When surveys discover that people make mistakes with information, the alleged ’cause’ is sometimes attributed to be a lack of numeracy and literacy skills in the users, and the ‘solution’ is to change people through education. But no amount of education will help when the public information itself is at fault. Our many projects suggest that the faults in routinely produced  public documents are such that less than 40% of the public can use them effectively.

Our job is not to test or change people but to change public information so people can use it. In our diagnostic testing we invite people to help us discover the specific faults in the information that makes it difficult or impossible to use. We begin by testing, with participants, the original public document. This reveals some of the worst symptoms. We redesign and retest it to see if people can now use it. If they can, we take this as evidence that our patient—the document—is cured. If we have not succeeded and the information is still unusable, we make further changes and retest repeatedly until people can use it. We call it ‘testing’ because we apply the process rigorously to detect faults in public documents, redesigning to fix the faults and retesting to see if the faults have disappeared.

The above description is an oversimplification, but it summarises the basic logic which drives our diagnostic work.

As designers, we are constantly changing the things we create and bringing new things into existence. Many of the things we create in communication and information design—such as forms, instructions, contracts, directions, bills, websites, and agreements—are the routine objects of daily life that people have to use. And as such we have a civic responsibility to ensure that the things we create are socially acceptable to the people who have to use them. Diagnostic testing is an act of politeness in civic society. At its heart it is a special type of conversation between information designers and the people who have to use their designs. The motive behind the conversation is social and practical.

The purpose of the conversation is to discuss the variety of things people may want to use a design for, whether they can use it for those purposes, and if not, what might be the reasons. We listen to what people say to us about the information being tested. But we do more than just ask questions: throughout the testing, we record and observe what people try to do with the information. We combine what they say and do with our knowledge of communication and  information design, using the combination to diagnose faults in the design and to work on ways to reduce the symptoms and cure the document.


While we were developing the methods of diagnostic testing and the detailed logic of its application, behavioural science researchers were developing usability testing. But our diagnostic testing grew out of a different intellectual tradition.

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The results of information designers doing their own testing has been profound. We report our findings on this through our Model Design Projects. In the next paper on Diagnostic Testing, I will explain the refinements we have made to our testing over the last 30 years.

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