The way people feel when using something is just as important as how they use it. In order to effectively evaluate a design, then, you may need to measure people’s subjective and objective feedback of an experience. To ensure reliability, the System Usability Scale (SUS) provides a good option. It is a freely available questionnaire originally developed by John Brooke for Digital Equipment Corporation. The SUS uses the Likert Scale, which asks participants to evaluate each question by choosing between five attitude responses, ranging from “Strongly Disagree” to “Strongly Agree.” This is a particularly effective way of benchmarking a given design against later iterations, and is highly versatile across many product and service realms.
To score the SUS, first subtract one point from the user response for each odd-numbered item. Then, for even-numbered items, subtract the user response from five. This scales all values from zero to four, with a four being the most positive response. Finally, add up the converted responses and multiply the total by 2.5. Any score above 68 is considered above average.