seven quality tools new

Ishikawa Seven Basic Tools

Sreenivas

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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

Ishikawa’s 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.

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.


• Creating a Histogram– Collect data and sort it into categories.– Then label the data as the independent set or

the dependent set.• The characteristic you grouped the data by would

be the independent variable.• The frequency of that set would be the dependent

variable.

– 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.


• 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 companies and wanted to compare numbers.

When to Use a Histogram • When the data are numerical. • When you want to see the shape of the data’s

distribution, especially when determining whether the output of a process is distributed approximately normally.

• When analyzing whether a process can meet the customer’s requirements.

• When analyzing what the output from a supplier’s 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 more processes are different.

• When you wish to communicate the distribution of data quickly and easily to others.

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.

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 each

particular value occurs, and their information is increasingly helpful as more data are collected.

• More than 50 observations should be available to be charted for this tool to be really useful.

• Check sheets minimize clerical work since the operator 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 specific location, 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 on results 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.

Because it clearly organizes data, a check sheet is the easiest way to track information.

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.

Check Sheet Procedure• Decide what event or problem will be observed.

Develop operational definitions. • Decide when data will be collected and for how long. • Design the form. Set it up so that data can be

recorded simply by making check marks or Xs or similar symbols and so that data do not have to be recopied for analysis.

• Label all spaces on the form. • Test the check sheet for a short trial period to be

sure it collects the appropriate data and is easy to use.

• Each time the targeted event or problem occurs, record data on the check sheet.

Check Sheet Example

The 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.

Phases of Software Development Process in a company

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.

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.

Create a Check Sheet

Track up to 10 defects on each day of the week.

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.

Pareto chart Also 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.

• 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 problems—most 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 management presentations.

• 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.

By rearranging random data, a Pareto diagram identifies and ranks nonconformities in the quality process in descending order.

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.


• Constructing a Pareto Chart– First, information must be selected

based on types or classifications of defects that occur as a result of a process.

– The data must be collected and classified into categories.

– Then a histogram or frequency chart is constructed showing the number of occurrences.

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 causes and 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.

Pareto Chart Examples

Example #1 shows how many customer complaints were received in each 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.

Example #2 takes the largest category, “documents,” from Example #1, breaks it down into six categories of document-related complaints, and

shows cumulative values.

Pareto Chart in Software Process

• Pareto analysis helps by identifying areas that cause most 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.

Figure shows an example of a Pareto analysis of the causes of defects for a product

Summary• A Pareto diagram is a frequency chart of bars in

descending 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, a Pareto 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 80–20 principle (20% of the causes account for 80% of the defects), although the cause-defect relationship is not always in an 80–20 distribution.

Scatter DiagramAlso called: scatter plot, X–Y graph

Definition:• The scatter diagram graphs pairs of

numerical data, with one variable on each 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.

• 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) axis represents 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 values on the x-axis and the corresponding quantitative measurement values on the y-axis.

The plotted data points in a scatter diagram show the relationship between two variables.

Scatter Diagrams

• Scatter Diagrams Defined– Scatter Diagrams are used to study

and identify the possible relationship between the changes observed in two different sets of variables.

Scatter Diagrams

• Constructing a Scatter Diagram– First, collect two pieces of data and create a

summary table of the data.– Draw a diagram labeling the horizontal and

vertical axes. • It is common that the “cause” variable be labeled on

the X axis and the “effect” variable be labeled on the Y axis.

– Plot the data pairs on the diagram.– Interpret the scatter diagram for direction

and strength.

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.

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.

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 with the 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 are discovered over a long time, the positive correlation between the two allows us to use program complexity to predict defect level.

• We can reduce the program complexity when it is developed (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 defects are clear indications of modules that are poorly designed or implemented and should also be scrutinized.

Scatter Diagram of Program Complexity and Defect Level

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 some effect is expected on the Y variable).

Cause and Effect DiagramsSlide 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.


• 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 more

specific causes.– View the diagram and evaluate the main causes.– Set goals and take action on the main causes.


• An Example of When a Cause and Effect Diagram Can Be Used– This diagram can be used to detect the problem of

incorrect deliveries.• Diagram on next slide

– Diagram obtained from: <http://www.hci.com.au/hcisite/toolkit/causeand.htm>

– When a production team is about to launch a new product, the factors that will affect the final product must be recognized. The fishbone diagram can depict problems before they have a chance to begin.


Diagram of the Incorrect Deliveries Example:

When to Use a Fishbone DiagramAlso Called: Cause-and-Effect Diagram, Ishikawa Diagram

• When identifying possible causes for a problem.

• Especially when a team’s thinking tends to fall into ruts.

Flow ChartsSlide 1 of 3

• Flow Charts Defined– A flow chart is a pictorial representation

showing all of the steps of a process.


• 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 don’t in the process of simplifying the work.


• 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

Run ChartsSlide 1 of 3

• Run Charts Defined– Run charts are used to analyze processes

according to time or order.


• 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 represent

time and values of Y represent the measurements taken from the manufacturing 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 the

process or operation.


• An Example of Using a Run Chart– An organization’s desire is to have their product arrive

to their customers on time, but they have noticed that it doesn’t 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.

Control ChartsSlide 1 of 3

• Control Charts Defined– Control charts are used to determine whether a

process will produce a product or service with consistent measurable properties.


• Steps Used in Developing Process Control Charts– Identify critical operations in the process where

inspection might be needed.– Identify critical product characteristics.– Determine whether the critical product characteristic is

a variable or an attribute.– Select the appropriate process control chart.– Establish the control limits and use the chart to monitor

and improve.– Update the limits.


• An Example of When to Use a Control Chart– Counting the number of defective products or

services• Do you count the number of defects in a given

product or service?

• Is the number of units checked or tested constant?

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.

Activity

• Process Flow Chart for Finding the Best Way Home– Construct a process flow chart by making the best

decisions 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 in the process.

» Answer is on the next slide» Example obtained from:

<http://deming.eng.clemson.edu/pub/tutorials/qctools/flowm.htm#Example>

Summary

This presentation provided learning material for each of Ishikawa’s seven basic tools of quality.

Each tool was clearly defined with definitions, a step-by-step process and an example of how the tool can be used.

As seen through the presentation, these tools are rather simple and effective.

Works - Cited

• Histograms and Bar Graphs. <http://www.shodor.org/interactivate/lessons/sm3.html>

• 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.

<http://http://deming.eng.clemson.edu/pub/tutorials/qctools/flowm.htm>• Run Charts/Time Plot/ Trend Chart.

<http://www.deming.edu.clemson.edu/pub/tutorials/qctools/runm.htm>• Foster Thomas S. Managing Quality An Integrative Approach. New Jersey:

Prentice Hall, 2001

http://yourmba.co.uk/pareto_diagram.htm

http://hci.com.au/hcisite/toolkit/causeand.htm

http://sytsma.com/tqmtools/Scat.html

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