Statistical analysis is gradually entering all areas of society, be in academia or in the private sector. Statistical software is used by statisticians but also by non-experts (medical doctors, psychologists...). Unfortunately, this kind of software is integrated into obsolete interfaces that completely ignore the principles of HCI and are poorly adapted to non-expert users.R++ project aims to develop a modern statistical analysis software program integrated into a user-friendly interface. In this paper, we present the methodology that led us to the design of R++. We also give two examples that this methodology allowed us to achieve.