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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 ~

### 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

### 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.

### 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

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### 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.

### 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.

### 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.

### 2.8.2 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.

### 2.8.3 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.

### 2.8.4 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.

### 2.8.5 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

### 2.8.6 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.

### 2.8.7 Activity Network Diagram

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