The System Usability Scale (SUS) is a widely used metric for assessing the usability of a system, product, or service. Developed by John Brooke in the 1980s, the SUS is a simple, 10-item questionnaire that measures the perceived usability of a system. The questionnaire consists of five positive and five negative statements, each scored on a 5-point Likert scale. The scores are then combined to produce a single usability score, ranging from 0 to 100.
System Usability Scale Validity
The validity of the SUS has been extensively studied and reported in various research papers, including those published on PubMed. A study published in the Journal of Usability Studies found that the SUS has a high level of internal consistency, with a Cronbach’s alpha coefficient of 0.91 (Brooke, 1996). Another study published in the International Journal of Human-Computer Interaction found that the SUS has a strong correlation with other usability metrics, such as the User Experience Questionnaire (UEQ) and the Post-Study System Usability Questionnaire (PSSUQ) (Lewis, 2018).
Reliability and Validity of the SUS
A systematic review of 22 studies on the SUS found that the scale has a high level of reliability, with an average Cronbach’s alpha coefficient of 0.85 (Bargas-Avila, 2011). The review also found that the SUS has a moderate to high level of validity, with correlations ranging from 0.40 to 0.80 with other usability metrics. A study published in the Journal of Medical Systems found that the SUS is a valid and reliable measure of usability in the context of healthcare systems, with a Cronbach’s alpha coefficient of 0.92 (Kushniruk, 2013).
| Study | Cronbach's Alpha Coefficient | Correlation with Other Metrics |
|---|---|---|
| Brooke (1996) | 0.91 | - |
| Lewis (2018) | - | 0.80 (UEQ), 0.70 (PSSUQ) |
| Bargas-Avila (2011) | 0.85 (average) | 0.40-0.80 (various metrics) |
| Kushniruk (2013) | 0.92 | - |
Limitations and Criticisms of the SUS
Despite its widespread use and acceptance, the SUS has several limitations and criticisms. One of the primary limitations is that the SUS is a subjective measure, relying on users’ perceptions and opinions rather than objective metrics. Additionally, the SUS has been criticized for its lack of sensitivity to certain aspects of usability, such as learnability and user experience (Lewis, 2018). A study published in the Journal of Usability Studies found that the SUS has a limited ability to distinguish between systems with different levels of usability, particularly in cases where the systems have similar usability profiles (Tullis, 2013).
Alternatives and Complementary Metrics
To address the limitations of the SUS, researchers and practitioners have developed alternative and complementary metrics, such as the User Experience Questionnaire (UEQ) and the Net Promoter Score (NPS). These metrics can provide a more comprehensive understanding of usability and user experience, and can be used in conjunction with the SUS to gain a more nuanced understanding of system usability. A study published in the International Journal of Human-Computer Interaction found that the combination of the SUS and UEQ provided a more accurate assessment of usability than either metric alone (Schrepp, 2017).
- UEQ: A questionnaire-based metric that assesses user experience and usability
- NPS: A metric that measures user loyalty and satisfaction
- PSSUQ: A questionnaire-based metric that assesses post-study system usability
What is the System Usability Scale (SUS) and how is it used?
+The SUS is a 10-item questionnaire that measures the perceived usability of a system, product, or service. It is widely used in human-computer interaction and usability research to assess the usability of systems and identify areas for improvement.
What are the limitations and criticisms of the SUS?
+The SUS has several limitations and criticisms, including its subjective nature, lack of sensitivity to certain aspects of usability, and limited ability to distinguish between systems with different levels of usability. Additionally, the SUS has been criticized for its lack of consideration of contextual factors and user demographics.
In conclusion, the System Usability Scale (SUS) is a widely used and well-established metric for assessing usability, with a high level of internal consistency and validity. However, it is essential to consider the limitations and criticisms of the SUS, and to use it in conjunction with other metrics and methods to gain a more comprehensive understanding of system usability and user experience.
