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Seven Quality Tools The Seven Tools
Histograms, Pareto Charts, Cause and
Effect Diagrams, Run Charts, Scatter
Diagrams, Flow Charts, Control Charts
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Ishikawas Basic Tools of Quality Kaoru Ishikawa developed seven basic visual
tools of quality so that the average person
could analyze and interpret data.
These tools have been used worldwide by
companies, managers of all levels and
employees.
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HistogramsSlide 1 of 3
Histogram Defined
A histogram is a bar graph that shows
frequency data.
Histograms provide the easiest way to
evaluate the distribution of data.
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Histograms
Slide 2 of 3 Creating a Histogram
Collect data and sort it into categories.
Then label the data as the independent set or thedependent set.
The characteristic you grouped the data by would be theindependent variable.
The frequency of that set would be the dependentvariable.
Each mark on either axis should be in equal
increments. For each category, find the related frequency and
make the horizontal marks to show that frequency.
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HistogramsSlide 3 of 3
Examples of How Histograms Can Be
Used
Histograms can be used to determine
distribution of sales.
Say for instance a company wanted to
measure the revenues of other companiesand wanted to compare numbers.
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When to Use a Histogram
When the data are numerical. When you want to see the shape of the datas distribution,
especially when determining whether the output of a process
is distributed approximately normally.
When analyzing whether a process can meet the customers
requirements. When analyzing what the output from a suppliers process
looks like.
When seeing whether a process change has occurred from one
time period to another.
When determining whether the outputs of two or moreprocesses are different.
When you wish to communicate the distribution of data quickly
and easily to others.
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Summary
The histogram is a graphic representation of
frequency counts of a sample or a population.
The X-axis lists the unit intervals of a parameter
(e.g., severity level of software defects) ranked
in ascending order from left to right, and the Y-
axis contains the frequency counts
The purpose of the histogram is to show the
distribution characteristics of a parameter
It enhances understanding of the parameter of
interest.
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Check List (Sheet)Also called: defect concentration diagram
Definition:
A check sheet is a structured, prepared form
for collecting and analyzing data. This is a
generic tool that can be adapted for a wide
variety of purposes.
Check sheets help organize data by category.
Check sheets show how many times eachparticular value occurs, and their
information is increasingly helpful as more
data are collected.
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More than 50 observations should be available to be
charted for this tool to be really useful.
Check sheets minimize clerical work since theoperator merely adds a mark to the tally on the
prepared sheet rather than writing out a figure (Figure
in next slide).
By showing the frequency of a particular defect (e.g.,
in a molded part) and how often it occurs in a specificlocation, check sheets help operators spot problems.
The check sheet example shows a list of molded part
defects on a production line covering a week's time.
One can easily see where to set priorities based onresults shown on this check sheet.
Assuming the production flow is the same on each day,
the part with the largest number of defects carries the
highest priority for correction.
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Because it clearly organizes data, a check sheet is the easiest
way to track information.
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When to Use a Check Sheet
When data can be observed and collected
repeatedly by the same person or at the
same location. When collecting data on the frequency or
patterns of events, problems, defects,
defect location, defect causes, etc.
When collecting data from a production
process.
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Check Sheet ExampleThe figure below shows a check sheet used to collect data on telephone
interruptions. The tick marks were added as data was collected over
several weeks.
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Phases of Software Development Process in acompany
The software development process consists of multiple phases:
1. Requirements (RQ),
2. System architecture (SD),
3. High-level design (HLD),
4. Low-level design (LLD),
5. Code development (CODE),
6. Unit tests (UT),
7. Integration and building (I/B),
8. Component tests (CT),9. System tests (ST), and
10. early customer programs (EP).
Each phase has a set of tasks to complete and the phases with
formal hand-off have entry and exit criteria.
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Check list in Software Process
Checklists help developers and programmers ensure that all
tasks are complete and that the important factors or
quality characteristics of each task are covered
Examples of checklists are
design review checklist,
code inspection checklist,
moderator (for design review and code inspection)
checklist,
pre-code-integration (into the system library) checklist, entrance and exit criteria for system tests, and
product readiness checklist.
Checklists are often a part of the process documents.
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Create a Check Sheet
Track up to 10 defects on each day of
the week.
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Summary
A check sheet is a paper form with printed items to
be checked.
Its main purposes is to facilitate gathering data and
to arrange data while collecting it so the data can
be easily used later.
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Pareto chartAlso called: Pareto diagram, Pareto analysis
Definition:
A Pareto chart is a bar graph. The lengths of
the bars represent frequency or cost (time or
money), and are arranged with longest bars on
the left and the shortest to the right. In this
way the chart visually depicts which
situations are more significant.
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The Pareto diagram is named after Vilfredo Pareto, a 19th-
century Italian economist who postulated that a large share of
wealth is owned by a small percentage of the population.
This basic principle translates well into quality problemsmost
quality problems result from a small number of causes.
Quality experts often refer to the principle as the 80-20 rule; that
is, 80% of problems are caused by 20% of the potential sources.
A Pareto diagram puts data in a hierarchical order (Figure in next
slide), which allows the most significant problems to be corrected
first.
The Pareto analysis technique is used primarily to identify and
evaluate nonconformities, although it can summarize all types of
data.
It is perhaps the diagram most often used in managementpresentations.
To create a Pareto diagram, the operator collects random data,
regroups the categories in order of frequency, and creates a bar
graph based on the results.
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By rearranging random data, a Pareto diagram identifies and ranks
nonconformities in the quality process in descending order.
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Pareto ChartsSlide 1 of 4
Pareto Chart Defined
Pareto charts are used to identify and prioritize
problems to be solved. They are actually histograms aided by the 80/20
rule adapted by Joseph Juran.
Remember the 80/20 rule states that approximately
80% of the problems are created by approximately 20%
of the causes.
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Pareto ChartsSlide 2 of 4
Constructing a Pareto Chart
First, information must be selected based
on types or classifications of defects thatoccur as a result of a process.
The data must be collected and classifiedinto categories.
Then a histogram or frequency chart isconstructed showing the number ofoccurrences.
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When to use a Pareto ChartSlide 3 of 4
When analyzing data about the frequency of
problems or causes in a process.
When there are many problems or causesand you want to focus on the most
significant.
When analyzing broad causes by looking at
their specific components.
When communicating with others about your
data.
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Pareto ChartsSlide 4 of 4
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Pareto Chart Examples
Example #1 shows how many customer complaints were received ineach of five categories.
If all complaints cause equal distress to the customer, working on
eliminating document-related complaints would have the most impact,
and of those, working on quality certificates should be most fruitful.
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Example #2 takes the largest category, documents, from Example #1,
breaks it down into six categories of document-related complaints, and
shows cumulative values.
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Pareto Chart in Software Process
Pareto analysis helps by identifying areas that causemost of the problems
Pareto analysis of software defects by category for
four Hewlett-Packard software projects.
The top three types new function or different processing required,
existing data need to be organized/ presented differently,
and
user needs additional data fields) account for more than
one-third of the defects. By focusing on these prevalent defect types, determining
probable causes, and instituting process improvements,
Hewlett-Packard was able to achieve significant quality
improvements.
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Figure shows an example of a Pareto analysis of the causes
of defects for a product
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Summary
A Pareto diagram is a frequency chart of bars indescending order
In software development, the X-axis for a Pareto diagram
is usually the defect cause and the Y-axis the defect
count
By arranging the causes based on defect frequency, aPareto diagram can identify the few causes that account
for the majority of defects
It indicates which problems should be solved first in
eliminating defects and improving the operation.
Pareto analysis is commonly referred to as the 8020
principle (20% of the causes account for 80% of the
defects), although the cause-defect relationship is not
always in an 8020 distribution.
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Scatter DiagramAlso called: scatter plot, XY graph
Definition:
The scatter diagram graphs pairs of
numerical data, with one variable oneach axis, to look for a relationship
between them. If the variables are
correlated, the points will fall along a
line or curve.
The better the correlation, the tighter
the points will hug the line.
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A scatter diagram shows how two variables are
related and is thus used to test for cause and
effect relationships. It cannot prove that one variable causes the
change in the other, only that a relationship
exists and how strong it is.
In a scatter diagram, the horizontal (x) axisrepresents the measurement values of one
variable, and the vertical (y) axis represents the
measurements of the second variable.
Figure in next slide shows part clearance valueson the x-axis and the corresponding quantitative
measurement values on the y-axis.
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The plotted data points in a scatter diagram show the relationship
between two variables.
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Scatter Diagrams
Scatter Diagrams Defined
Scatter Diagrams are used to study and
identify the possible relationship betweenthe changes observed in two different sets
of variables.
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Scatter Diagrams
Constructing a Scatter Diagram
First, collect two pieces of data and create asummary table of the data.
Draw a diagram labeling the horizontal andvertical axes.
It is common that the cause variable be labeled on the Xaxis and the effect variable be labeled on the Y axis.
Plot the data pairs on the diagram.
Interpret the scatter diagram for direction andstrength.
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Scatter Diagrams
An Example of When a Scatter Diagram
Can Be Used
A scatter diagram can be used to identify
the relationship between the production
speed of an operation and the number of
defective parts made.
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When to Use a Scatter Diagram
When you have paired numerical data.
When your dependent variable may have multiple values for
each value of your independent variable.
When trying to determine whether the two variables are
related, such as
When trying to identify potential root causes of problems.
After brainstorming causes and effects using a fishbone
diagram, to determine objectively whether a particular
cause and effect are related.
When determining whether two effects that appear to be
related both occur with the same cause.
When testing for autocorrelation before constructing a
control chart.
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Scatter Diagram in Software
Compared to other tools, the scatter diagram is
more difficult to apply. It usually relates to
investigative work and requires precise data
Scatter diagram usually illustrates the relationship
between complexity index and defect level
Each data point represents a program module withthe X coordinate being its complexity index and the
Y coordinate its defect level
Program complexity can be measured as soon as the
program is complete, whereas defects arediscovered over a long time, the positive correlation
between the two allows us to use program
complexity to predict defect level.
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We can reduce the program complexity when it isdeveloped (as measured by McCabe's index),
thereby reducing the chance for defects.
Reducing complexity can also make programs easier
to maintain.
Program modules with high-complexity indexes are
the targets for analysis and possible module
breakup, encapsulation, intramodule cleanup, and
other actions.
Low-complexity indexes coupled with high defectsare clear indications of modules that are poorly
designed or implemented and should also be
scrutinized.
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Scatter Diagram of Program Complexity and Defect Level
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Summary
A scatter diagram vividly portrays the
relationship of two interval variables.
Scatter diagrams aid data-based
decision making (e.g., if action is
planned on the X variable and someeffect is expected on the Y variable).
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Cause and Effect Diagrams
Slide 1 of 4
Cause and Effect Diagram Defined The cause and effect diagram is also called the Ishikawa diagram
or the fishbone diagram. It is a tool for discovering all the possible causes for a particular
effect.
The major purpose of this diagram is to act as a first step in
problem solving by creating a list of possible causes.
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Cause and Effect Diagrams
Slide 2 of 4
Constructing a Cause and Effect Diagram First, clearly identify and define the problem or effect for which
the causes must be identified. Place the problem or effect at the
right or the head of the diagram. Identify all the broad areas of the problem.
Write in all the detailed possible causes in each of the broad areas.
Each cause identified should be looked upon for further morespecific causes.
View the diagram and evaluate the main causes. Set goals and take action on the main causes.
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Cause and Effect Diagrams
Slide 3 of 4
An Example of When a Cause and Effect DiagramCan Be Used
This diagram can be used to detect the problem ofincorrect deliveries.
Diagram on next slide
Diagram obtained from:
When a production team is about to launch a newproduct, the factors that will affect the final productmust be recognized. The fishbone diagram can depict
problems before they have a chance to begin.
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Cause and Effect Diagrams
Slide 4 of 4
Diagram of the Incorrect Deliveries Example:
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When to Use a Fishbone DiagramAlso Called: Cause-and-Effect Diagram, Ishikawa Diagram
When identifying possible causes for aproblem.
Especially when a teams thinking tends to
fall into ruts.
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Flow Charts
Slide 1 of 3
Flow Charts Defined
A flow chart is a pictorial representation
showing all of the steps of a process.
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Flow Charts
Slide 2 of 3
Creating a Flow Chart
First, familiarize the participants with the flow chart
symbols. Draw the process flow chart and fill it out in detail
about each element.
Analyze the flow chart. Determine which steps add
value and which dont in the process of simplifying the
work.
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Flow Charts
Slide 3 of 3
Examples of When to Use a Flow Chart
Two separate stages of a process flow chart
should be considered: The making of the product
The finished product
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Run Charts
Slide 1 of 3
Run Charts Defined
Run charts are used to analyze processes
according to time or order.
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Run Charts
Slide 2 of 3
Creating a Run Chart Gathering Data
Some type of process or operation must be available to take measurements
for analysis. Organizing Data
Data must be divided into two sets of values X and Y. X values representtime and values of Y represent the measurements taken from themanufacturing process or operation.
Charting Data
Plot the Y values versus the X values. Interpreting Data
Interpret the data and draw any conclusions that will be beneficial to theprocess or operation.
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Run Charts
Slide 3 of 3
An Example of Using a Run Chart
An organizations desire is to have their product arrive
to their customers on time, but they have noticed that itdoesnt take the same amount of time each day of the
week. They decided to monitor the amount of time it
takes to deliver their product over the next few weeks.
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Control Charts
Slide 1 of 3
Control Charts Defined
Control charts are used to determine whether a
process will produce a product or service withconsistent measurable properties.
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Control Charts
Slide 2 of 3
Steps Used in Developing Process Control Charts
Identify critical operations in the process whereinspection might be needed.
Identify critical product characteristics.
Determine whether the critical product characteristic isa variable or an attribute.
Select the appropriate process control chart.
Establish the control limits and use the chart to monitorand improve.
Update the limits.
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Control Charts
Slide 3 of 3
An Example of When to Use a Control
Chart
Counting the number of defective products orservices
Do you count the number of defects in a given
product or service?
Is the number of units checked or tested constant?
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When to Use a Control Chart
When controlling ongoing processes by finding and correcting
problems as they occur.
When predicting the expected range of outcomes from a
process.
When determining whether a process is stable (in statistical
control).
When analyzing patterns of process variation from special
causes (non-routine events) or common causes (built into the
process). When determining whether your quality improvement project
should aim to prevent specific problems or to make fundamental
changes to the process.
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Activity Process Flow Chart for Finding the Best Way
Home
Construct a process flow chart by making the bestdecisions in finding the best route home.
Refer to the prior notes on flowcharts. Remember: Define and analyze the process, build a step-by
step picture of the process, and define areas of improvement inthe process.
Answer is on the next slide
Example obtained from:
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SummaryThis presentation provided learning material for each of Ishikawasseven basic tools of quality.
Each tool was clearly defined with definitions, a step-by-step processand an example of how the tool can be used.
As seen through the presentation, these tools are rather simple andeffective.
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Works - Cited Histograms and Bar Graphs.
Your MBA: The Business Study Reference Site.http://yourmba.co.uk/pareto_diagram.htm
Hci Home Services. Cause and Effect Diagram.http://hci.com.au/hcisite/toolkit/causeand.htm
Scatter Diagram. http://sytsma.com/tqmtools/Scat.html
Flowchart.
Run Charts/Time Plot/ Trend Chart.
Foster Thomas S. Managing Quality An Integrative Approach. New Jersey:
Prentice Hall, 2001