System, Intervention, and Implementation Strategy Usability Scales (SUS/IUS/ISUS)

The Intervention Usability Scale (IUS), Implementation Strategy Usability Scale (ISUS), and System Usability Scale (SUS) are a set of related scales that support assessment of the usability of interventions, implementation strategies, and systems, where a system may be software program or paper form.

This can support decisions like whether a prototype is ready to advance to more widespread testing or comparisons, such as whether a redesigned intervention is more usable than the original intervention. While they can help answer how usable something is, the scales on their own do not directly guide how to redesign something to be more usable.  

Should you use the System, Intervention, or Implementation Strategy Usability Scale?

Overall, our guidance parallels the name of each scale. If your goal is to assess the usability of the intervention (including any associated supporting tools), then use the Intervention Usability Scale (IUS). If your goal is to assess the usability of a system or artifact, use the System Usability Scale (SUS). SUS was developed primarily for digital systems but may work for other kinds of artifacts such as worksheets. 

There may be times when you need to assess two or all three. However, in these instances, we recommend against using SUS and IUS in the same session with the same participants, as the similarities may lead to fatigue or confusion. Further, because UWAC projects are often investigating the usability of an intervention and usability of a system, it is important for the object or target of the survey to be clear. 

Role of scales in each DDBT phase: When and how to use them 

Even if you use the same scale in each phase, it may have different roles. 

Discover and Test Phases 

From the center perspective, we hope to collect or set up comparisons between the usability of the un-adapted intervention or implementation strategy and the redesigned intervention or implementation strategy, among the intended users and in the intended population. Example comparisons include: 

• Comparing an un-adapted intervention in discover phase to the redesigned intervention in the test phase using the IUS 
• In a project with a test phase that has a control condition of the un-adapted intervention/implementation strategy, comparing usability of the un-adapted intervention/implementation strategy (control group) with the adapted intervention/implementation strategy (redesign group) by comparing the IUS/ISUS scores between the control and redesign groups after a period of use in the test phase. 
• In a project that focuses on redesigning an artifact-based intervention strategy (e.g., software, paper form) to improve usability, comparing the artifact’s usability between the discover phase and test phase using SUS.  

Projects where the un-adapted intervention or implementation strategy cannot be used at all in the destination context without adaptation can prevent collecting meaningful IUS/ISUS/SUS data at this stage. In this situation, please reach out to the Methods Core to discuss what might be useful for both your project and center goals. 

Design Build / Phase 

Teams also may use IUS/ISUS/SUS to assess usability during the design/build phase. Early in this process, a scale might be used with scenarios or storyboards to assess perceived or anticipated usability of a design direction. Interviewers might probe about responses to items that indicate potential usability issues to guide redesign. Later, as prototypes mature, participants can complete the IUS/ISUS/SUS after doing a set of tasks (e.g., using the system or role-playing steps in an intervention or implementation strategy). Usability experts tend to look for a SUS score to reach 70 (a benchmark for satisfactory usability) before moving to a test phase, as doing so earlier will likely mean that significant usability issues remain that would interfere with overall goals for a test phase. It is not known if a similar benchmark carries over to the newer IUS/ISUS. This guide provides further detail on interpreting SUS scores.  

The shorter Usability Metric for User Experience (UMUX) (4-item) or (UMUX-Lite) 2-item might also be used in this iterative process, to avoid measurement fatigue. UMUX-Lite correlates well with SUS, at least for evaluation of technologies – but to convert between UMUX-Lite and SUS, you must use 7-point Likert scales. Currently, there are not published examples of using UMUX or UMUX-Lite for non-digital interventions and implementation strategies. 

As teams wrap up the design/build phase, participants must complete the IUS/ISUS/SUS about their redesigned intervention or implementation strategy. Please report this (and not all iterations) to the center, as we would like to know what usability level is reached by the end of design. 

Adapting the Wording of Scale Items

Before administering the survey, review—and possibly pilot—your selected scale to assess if the wording of items is appropriate for your participants and what you are evaluating. Sometimes, it can make sense to adapt items – you are welcome to meet with the Methods Core to discuss possible adaptations or adding clarifications. Please meet with the Methods Core before dropping items or changing the response scale, as this can inhibit later comparisons with other projects. 

If you need to translate the scale into a different language, the translated scale should be piloted and discussed with community partners. A protocol you can consider using for translating IUS/ISUS/SUS is A systematic approach for accurate translation of instruments: Experience with translating the Connor–Davidson Resilience Scale into Arabic (Toma et al., 2017), which has also been used to translate AIM/IAM/FIM. 

Example of SUS adapted for children and additional examples of SUS adaptations.