An important measure of design quality is the extent to which a circuit design is able to meets its specification in the presence of component parameter variations. Of equal importance is knowing how to improve this capability most effectively. This paper presents an analysis technique and visualization method which give the designer information about design quality and possible routes to improved quality. The paper introduces two new measures of functional capability, based on the process capability measure C-pk, and shows how these may be linked to the statistical variations in individual component parameters. It then shows how this information may be used to assess the effectiveness of altering the nominal value and variability in each of the component parameters in order to improve circuit performance capability. The analysis required is straightforward and the information is presented in a clear manner which can readily be interpreted by the designer. The effectiveness of the technique has been evaluated through analysis of a number of printed circuit board level analogue and mixed signal circuits and the results of a case study are shown. Copyright (C) 2007 John Wiley & Sons, Ltd.