This was a good summary of these tools, but in my humble opinion, you left out a very important one: The process control chart, AKA process behavior chart. Without that, you cannot know whether your Pareto chart is any good (what if the largest bar is that large because of a special cause--especially if it's one that's already been addressed). The histogram has little meaning if the data were not homogeneous; if it's a histogram of a time-ordered process, you need to find out whether that process was stable. If it's trending over time or if the process has shifted, the histogram will not be representative. Control charts should be used to baseline the process data, to check the results of pilots, to detect differences after improvements are made; they can also be used with process data in place of one-way ANOVA or t-tests, to find differences between production lines/processes or before-after testing. Unfortunately, a lot of the Six Sigma literature now relegates control charts to the CONTROL phase, and they are treated as an afterthought, when they should be the basis of any good project. I've seen Six Sigma textbooks that would have us running capability studies without running process behavior charts first.