The 7 indispensable quality control tools

The “Seven Basic Tools of Quality” is a name given to a fixed set of graphical techniques, first emphasized by Dr. Kaoru Ishikawa, a professor of Engineering at Tokyo University, Japan, popularly known as the father of “Quality Circles.” Ishikawa was inspired by the seven famous weapons of Benkei, a Japanese warrior monk who is commonly depicted as a man of great strength and loyalty in Japanese folklore.

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Quality professionals consider these tools as most helpful in troubleshooting issues. They are called basic tools because they are suitable for people with little formal training in statistics and because they can be used to solve the vast majority of quality-related issues.

#1 Cause-and-effect diagram

Also known as Ishikawa diagram as it was originally created and used by Dr. Kaoru Ishikawa. Because of its shape, it’s also called a fishbone diagram. This helps in identifying many possible causes for a problem, and sorts ideas into useful categories. Understand how to use a fishbone diagram with this awesome course

#2 Check sheet (tally sheet)

A check sheet is a structured document which can be used for metrics and is used to collect data in real-time and analyzing it. A check sheet is also called a tally sheet when the information collected is quantitative in nature. The very purpose of this is to list down the important checkpoints or events in a tabular/metrics format and keep updating or marking the status of their occurrence which helps in understanding the progress, defect patterns, and even causes for defects.

#3 Control charts

Control charts are graphs used to study how a process changes over time. These are the most difficult to use out of the seven tools. Hence, control charts are seldom the tool of choice for most quality professionals. When a process step is important, professionals prefer that the step not vary at all.

#4 Histogram

Histograms were introduced by Karl Pearson, an influential scholar of statistics. A histogram is a bar graph representing the frequency distribution, or how often each different value in a set of data occurs, on each bar. It is created by grouping the data you collect into “cells” or “bins.” The histogram is the most commonly used graph for showing frequency distributions. 

#5 Pareto chart

Pareto charts are a specialized histogram of count data. This is used to show which factors are more significant on a bar graph. Pareto chart derives its name from the use of the Pareto Principle which states “80% of the effect comes from 20% of the causes.” Vilfredo Pareto, an Italian economist, originated this principle by determining that 80% of the land in Italy was owned by 20% of the population. Later, it was found to hold true in many things and helps us focus on the critical few. With this chart, professionals can decide where to place priority and focus. This is extremely helpful when time and money are limited.

#6 Scatter diagram

A scatter diagram is a very simple tool to know if there is a correlation between two things (i.e., does one thing lead to another?). It depicts dependent variables on the Y axis and independent variables on the X axis, plotted as dots on their common intersection points. 

#7 Stratification

Stratification is a method of dividing data into subcategories and classifying data based on group, division, class, or levels that helps in deriving meaningful information to understand an existing problem. A technique that separates data gathered from a variety of sources so that patterns can be seen (some lists replace “stratification” with “flowchart” or “run chart”).

Manufacturing professionals, you can now start your quality journey by mastering these tools.

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