Chapter 2 basic tools for improving quality
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Chapter 2 Basic Tools for Improving Quality. 7 Basic Tools by Ishikawa. Histogram Pareto chart Scatter plot Control chart Cheek sheet Cause-and-effect diagram Defect concentration diagram. 2.1 Histogram.

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Chapter 2 Basic Tools for Improving Quality

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Chapter 2Basic Tools for Improving Quality

7 Basic Tools by Ishikawa

  • Histogram

  • Pareto chart

  • Scatter plot

  • Control chart

  • Cheek sheet

  • Cause-and-effect diagram

  • Defect concentration diagram

2.1 Histogram

  • A histogram is a bar chart that shows the relative frequencies of observations in each of several classes.

  • Rule for determining the number of classes:

    • “Power of 2 rule”: for n observations, we would use a classes, where 2a-1 < n < 2a

    • Roundup a = lnn / ln 2 (=ROUNDUP(LN(100)/LN(2), 0)

    • a ~

Table 2.1 Example Data

Histogram by Minitab

Histogram by Excel

2.2 Pareto Charts

  • A Pareto chart is a bar graph that shows the relative frequencies of observations in a descending order.

    • draws its name from an Italian economist, VilfredoPareto (1848–1923)

    • J. M. Juran is credited with being the first person to apply it to industrial problems

Table 2.3 Nonconformities and Associated Monetary Losses

Pareto Chart on Nonconformities

Pareto Chart on Monetary Losses

2.3 Scatter Plots

  • A scatter plot is another simple graphical device

  • The simplest type is a bivariate scatter plot, in which two quantities are plotted.

  • Scaling of the two axes is somewhat arbitrary

  • A time sequence plot is a type of scatter plot in that data on one variable are plotted against a second variable, time.

  • A probability plot is another type of scatter plot.

Table 2.4 Data for Quality Improvement Program

Table 2.4 Data for Quality Improvement Program

Variations of Scatter Plots

  • Use number or special symbols for duplicated data points.

  • Use “range frames”, instead of scales

2.4 Control Charts

  • A control chart is a time sequence plot with “decision lines” added.

  • These decision lines are used to try to determine whether or not a process is in control.

    • Type I and II errors











Typical Control Chart






















Sample number

2.5 Check Sheet

  • A check sheet is a means of recording historical data on causes of nonconformities or nonconforming units.

    • The general idea is to record all pertinent information relative to nonconformities and nonconforming units, so that the sheets can facilitate process improvement.

    • Such information might include notes on raw materials, machine performance, or operator changes.

2.6 Cause-and-Effect Diagram

  • The cause-and-effect diagram was introduced in Japan in 1943 by Professor Kaoru Ishikawa of the University of Tokyo.

    • For that reason it is sometimes called an Ishikawa diagram; it has also been called a fishbone chart.

Cause-and-Effect Diagram

2.7 Defect Concentration Diagram

  • It is simply a schematic diagram that shows the various sides of a unit of production, with the positions where nonconformities occur pinpointed.

Defect Concentration Diagram

2.8 The 7 Newer Tools

  • Affinity Diagram

  • Interrelationship Digraph

  • Tree Diagram

  • Prioritization Matrix

  • Matrix Diagram

  • Process Decision Program Chart

  • Activity Network Diagram

2.8.1 Affinity Diagram

  • An affinity diagram is a set of ideas about a particular topic that are grouped into clusters.

  • The diagram is the end product of brainstorming that is performed in a prescribed manner.

2.8.1 Affinity Diagram

2.8.2 Interrelationship Digraph

  • An interrelationship digraph is used for identifying and exploring causal relationships between related ideas.

  • This is a step beyond an affinity diagram, as an interrelationship digraph is a figure with arrows indicating relationships between ideas.

2.8.2 Interrelationship Digraph

2.8.3 Tree Diagram

  • A tree diagram is somewhat similar to a cause-and-effect diagram in that a desired effect (e.g., reducing delivery delays) can be shown pictorially as related to the factors that can lead to the effect.

  • A tree diagram will generally more closely resemble a company organizational chart in appearance than a cause-and-effect diagram.

  • A tree diagram is a more structured display than either an affinity diagram or an interrelationship digraph.

2.8.3 Tree Diagram

2.8.4 Prioritization Matrix

  • A prioritization matrix is a relative ranking of issues jobs, objectives, products, and so on.

  • The ranking is accomplished by comparing the components pairwise so that a logical and consistent ranking results.

2.8.4 Prioritization Matrix

2.8.5 Matrix Diagram

  • A matrix diagram is used for showing relationships between two or more sets of ideas, projects, and so on.

  • The matrix can have one of several different forms.

  • At least five forms have been used:

    • C-shaped

    • L-shaped

    • T-shaped

    • X-shaped, and

    • Y-shaped

2.8.5 Matrix Diagram

2.8.6 Process Decision Program Chart

  • A process decision program chart is a listing of undesirable events and corresponding contingency actions relative to planned actions.

  • It is used when there is considerable concern about the possibility of negative unanticipated outcomes.

2.8.6 Process Decision Program Chart

2.8.7 Activity Network Diagram

  • This is essentially a combination of two well-known techniques: PERT (Program Evaluation and Review) and CPM (Critical Path Method).

2.8.7 Activity Network Diagram

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