Seven Quality Control Tools

Seven QC Tools are diagrams which are utilized for analysis in quality control. These include Graph, Histogram, Control Chart, Check Sheet, Pareto Chart, Cause and Effect Diagram, Scatter Diagram. (QC: Quality Control)


1. Overview

In QC activities, members of the group work on solving concrete problem in business, consider measures to properly maintain the quality, to make work efficient, to develop human resources, to reduce costs , and so on, and practice them. In addition to that, procedures for solving problems called QC stories are defined so that workers in production field, who are not professional of problem solving, can analyze the current status scientifically.
The tools for problem solving utilized in these procedures are called seven QC Tools.


2. Purpose

The seven QC tools can also be used for analysis of activities data on Business Process Management activity (BPM activity). You can make use of those tools for finding problems of daily business and solving them.

Graph represents data visually by using figures such as circles and polygons.

It can represent data for special purpose in percentages and tendencies. e.g. Bar chart, Line chart, Circle chart, etc.

HistogramHistogram represents data distribution using bar chart. Frequency Distribution graph.

Dividing data range into appropriate interval, tabulate the number of data in each interval. The vertical axis represents the frequency, and the horizontal axis represents data section. We can grasp characteristics of tasks or products based on the center of the data distribution and the degree of variance.

control-chartControl chart represents the transition of an item and shows whether the item is under control or not.

By grasping transitions, we can detect occurrences of abnormal situations in advance, and can deal with them. Allowing the variation to some extent, we can estimete that the item is under control as long as fluctuating between the upper control limit (UCL) and the lower control limit (LCL).

check-sheetCheck Sheet is a table listing check items.

When inspecting products and equipments, this sheet enables us to perform inspections exhaustively or grasp the total number of inspections.

In addition, the inspecting results of Check Sheet can be used as data.

abc-analysisPareto Chart is a graph that bar charts which represent each item are sorted from left side in descending order of values, and that the cumulative frequency distribution curve (a line connecting the cumulative percentages up to each item) is also drawn.

By drawing Pareto Chart, we can grasp to which degree each item have influence on the results. Concerning items with large impact, we can effectively manage them by applying different ways of management depending on the significance, for example, by intensively managing them as important management items. In general, items of which cumulative proportions reach approximately 80% are considered as important management items. (ABC analysis : Activity Based Costing analysis )

Cause-and-EffectCause and Effect Diagram is a diagram which systematically represents the relations among effects and causes that affect them by using arrows.

By clarifying the relationship of factors that caused results or problems, we can clarify the subject to be improved. Dimensions must be aligned, and the ends need to be subdivided until concrete countermeasures can be taken. Effects are subjects to look for causes and comprise problems and results. After improvement items are determined, we need to enumerate the factors that are considered to be related to the items, and thereby clarify the relationship.

Scatter-diagramScatter Diagram is a diagram in which data of two items are plotted.

This helps us grasp whether there is any relation among items and how the items are related to each other. For example, in case the plots are largely distributed, we can say that there is no strong correlation between the two items.


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