Quality Control is defined as the "process of monitoring and recording the results of executing quality activities to assess performance and recomment necessary changes".
Quality Assurance, on the other hand, involves auditing results obtained from the quality control measurements to ensure that the approriate quality standards and being used (PMBOK 4th ed.).
Achieving high quality, thus invovles a close interworking between Quality Control (gathering results from what we're doing) and Quality Assurance (studying the data gathered to make sure we're doing everything as decided).
The ASQ defines 7 tools that allow proper representation of measurements to facilitate further analysis and perform quality assurance and quality control.
1) Ishikawa diagram: used to identify as many possible causes for a problem
2) Check sheet: used to gather data, by human observation, usually in realtime
3) Control chart: this graph represents process behaviour over time
4) Histogram: this depicts the frerquency of occurance of each measurement value
5) Pareto chart: a form of the histogram where data is sorted in descending order
6) Scatter diagram: used to check for correlations between two sets of data
7) Stratification: a technique to seperate data into related groups
Several sources often replace Stratification with Flow Chart/ Run chart as one of the tools.
7+) Flow chart / Run chart: pictorial representation of methods used to achieve a result.
Although all the above 7 tools are used in varying degrees for representation and analysis of measurements, it is important to understand their unique capabilities and advanatages. Hence, selecting the right tool(s) depending on the situation is critical to derive highest efficiency from Quality Control and Quality Assurance.
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