Companies work hard to differentiate from the competition and to build lasting customer loyalty through brands. We compare two existing methods for designing and analysing product family identity. As a result of the analysis, we merged the two methods and created a new method of four-dimensional design analysis. The method is used to analyse design elements used in existing product families. To investigate the actual effect that these design elements have on the perceived similarity of design, a two phase statistical analysis was performed. It was found that colour, shape, pattern, and texture all contribute significantly to the perceived similarity, but by different degree. Further, the perceived similarity can be enhanced by using more than one design element at a time.