A method for applying design for reliability into design for Six Sigma is described. The method includes establishing an appropriate model for reliability as a function of time; determining a reliability transfer function; calculating defects per opportunity per unit of time; entering said defects per opportunity per unit of time into a calculation of value of sigma; selecting one or more noise factors likely to have an impact on reliability; and performing a closed form analytical solution of said impact on reliability using a Monte Carlo analysis. The noise parameters may include one or more assumptions of the hours of usage per year, temperature of use, material quality, part quality, layout of components, extrinsic stresses, supplier quality, interconnection quality, test coverage, shipping damage, installation errors, errors in instructions, customer misuse or other noise factors beyond the control of the designer.