Hi Shree , In places where the root cause and result can be found out using 8D , there is no need to use 6sigma methodology. So , the first approach is always 8D , and still if we find that we are not able to come to the root cause and the problem still remains then we take the 6sigma approach imperatively . thnx .. Regards; Sankhasubhra Adhikari Quality Analyst - Lead Firstsource Solutions Ltd .