7 Quality Tools, Why 7?

A criterion shared unanimously by the experts in Quality Management is that most improvement projects can be carried out successfully using very simple data collection and analysis tools that are available to everyone.

These tools, simple but enormously versatile and useful, were compiled and disseminated in Japan by Dr Kaoru Ishikawa and later spread all over the world with the name of “basic tools for quality improvement” or, also, “the 7 Ishikawa’s basic tools. ” In Ishikawa’s text: “Quality Control Guide”, is the origin of what has been spread and disseminated in a thousand different ways.

It consists of the following tools:

  1. Cause-effect diagram, also called Ishikawa diagram or fishbone: graphic and simple representation to quickly see what are the causes, problems or spines to analyze, and how they relate to the problem or effect.
  2. Data collection sheet: how to collect and classify data according to certain categories, by recording and recording their frequencies
  3. Histogram: graphic representation of the data that indicates the shape of the distribution and possible symptoms (anomalies, asymmetry, bimodality, …)
  4. Pareto diagram (80-20 rule): Tool that allows prioritizing actions. According to Vilfredo Pareto, Italian economist, “80% of the problems can be solved, if 20% of the causes that originate them are eliminated”.
  5. Stratification: categorization of information in different states (shifts, machine, departments, type of product / service, …)
  6. Scatter diagram: graphical tool that allows you to see if there is any kind of relationship between 2 continuous variables. Calculating the correlation coefficient you can see the degree of relationship between both as well as its meaning (positive or negative)
  7. Control chart: statistical process control (SPC) tool, used to evaluate the stability of a process and detect the special causes of variation.

In the literature or 6 Sigma courses or problem solving, variants are observed as to what are the 7 quality tools. In the initial proposal of Ishikawa:

  • The Brainstorming was not part of these tools but usually appears naturally associated with cause-effect diagrams
  • The technique of control graphics is one of the tools but, due to its size, it is usually reserved an exclusive chapter of statistical process control (SPC) to explain it.

And why 7?

It seems to be related to Japanese mythology, in which number 7, in addition to being a lucky number, also corresponds to the number of basic pieces that comprise a team of samurai warrior when entering battle.