QC Tools & Techniques

December 7, 2009

There are about ten tools that has been indicated as useful in the PMBOK, for the QC process. The first seven tools are also known as Ishikawa’s seven basic tools of quality. In this part 1 of the articles on QC tools and techniques, the five tools out of the seven are discussed. The balance two and the three other tool/techniques such as statistical sampling, inspections and review of approved change requests besides the balance two of the Ishikawa’s tools are discussed in part 2 of this set of articles.

The Tools & Techniques

Cause & effect diagram helps in root cause analysis. They can also help identify risks in the project. A line drawn leading to major defect is the main focus. You drawing groups of causes along the top & bottom of the line The leading lines are drawn slanted. The overall diagram then looks like a fishbone. You can take any set of causes and expand the analysis by asking a series of how or why questions. Such “how-how” or “why-why” detailed diagrams will help identify the root cause easily.

Control charts that plot a series of desired values that also show a upper and lower acceptable limits are a good tool to determine if a process is within control. The chart also includes the upper and the lower control lines. These are tighter that the limit range and indicate if a process is showing undue variations or drifting one way that is a trend to exceed control limits.

Flowcharting is a graphic tool that clearly indicates the process steps and the decision points. The process and its behavior is clearly understood so that qc activities can discover either a failing step or opportunities for improvements.

Histogram is a vertical bar chart of how often a variable state occurred. For example, one may chart the frequency of different types of defects that occur. These may not be done in any particular order. But as they stand side by side the bars clearly show which the more frequent types of defects are. This can easily focus on investigating the reasons for the types that record a higher occurrence.

The Pareto chart or the Pareto diagram is also a histogram but drawn in a specific way. Staring from left you draw the highest bar first, then the next highest and so on. You also draw a line graph that shows the cumulative frequency as each type of defect is considered. You continue to add another bar graph until you have reached close to 80% cumulative % point. The bars included under the cumulative curve are the most significant causes of defect.

This comes from the Pareto principle that 80 % of problems are usually caused by 20% of the causes. We kept adding the causes and their effects until we accounted for 80% of the defects. These 5/6 or whatever cause we now have under the cumulative curve are the most significant causes cause most of the defects. You thus have arrived at clear issues to investigate further and determine how to eliminate them.

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