How the validity of an emerging design method or methodology, such as relative reliability risk index (R3I), should be tested and demonstrated remains a vital question for the design research community. This paper provides a review of current thinking about the validation process and via a case study seeks to describe how an appropriate controlled experiment was developed to address the validation of a particular methodology. The experimental validation approach described here is shown to be linked to the impact model of research and is built upon the foundations of validation square. The results of this approach to validation suggest that a standard approach to validating emerging design methods is possible. This is illustrated here by demonstrating that an improvement in the quality of evaluating concept designs can be obtained when using the R³I evaluation methodology.