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Chapter 2 Basic Tools for Improving Quality

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Chapter 2Basic Tools for Improving Quality

- Histogram
- Pareto chart
- Scatter plot
- Control chart
- Cheek sheet
- Cause-and-effect diagram
- Defect concentration diagram

- 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 ~

- 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

- 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.

- Use number or special symbols for duplicated data points.
- Use “range frames”, instead of scales

- 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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- 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.

- 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.

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

- Afﬁnity Diagram
- Interrelationship Digraph
- Tree Diagram
- Prioritization Matrix
- Matrix Diagram
- Process Decision Program Chart
- Activity Network 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.

- 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.

- 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.

- 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.

- 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

- 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.

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