1. Bradner, E. (2010,). Recommending net promoter. Retrieved on 23.10.2011 from DUX: Designing the User Experience at Autodesk .
2. Reichheld, F. (2003). The one number you need to grow. Harvard Business Review.
3. Answering the ultimate question;Owen,2008
4. Sauro, J. (2011). Usability and net promoter benchmarks for consumer software. Retrieved on 23.10.2011 from Measuring Usability .
5. Sauro, J., & Kindlund, E. (2005). Using a single usability metric (SUM) to compare the usability of competing products. In Proceeding of the human computer interaction international conference (HCII 2005), Las Vegas, NV.