Doc 17 Seven Quality Control Tools Part Ii

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Details on Seven QC Tools CQA Doc No 17 SCATTER DIAGRAM

A Scatter Diagram is used to interpret data by graphically displaying the relationship between two variables. A Scatter Diagram Is Used For: 1. Validating "hunches" about a cause-and-effect relationship between types of variables (examples: I wonder if students who spend more time watching TV have higher or lower average GPA's?; is there a relationship between the production speed of an operator and the number of defective parts made?; is there a relationship between typing speed in WPM and errors made?) 2. Displaying the direction of the relationship (positive, negative, etc.) (Examples: Will test scores increase or decrease if the students spend more time in study hall?; will increasing assembly line speed increase or decrease the number of defective parts made?; do faster typists make more or fewer typing errors?) 3. Displaying the strength of the relationship (examples: How strong is the relationship between measured IQ and grades earned in Chemistry?; how strong is the relationship between assembly line speed and the number of defective parts produced?; how strong is the relationship between typing faster and the number of typing errors made?) Steps In Constructing A Scatter Diagram: 1. Collect two pieces of data (a pair of numbers) on a student, process, or product. Create a summary table of the data. 2. Draw a diagram labelling the horizontal and vertical axes. It is common that the "cause" variable is labelled the horizontal (X) axis and the "effect" variable is labelled the vertical (Y) axis. The values should increase up the vertical scale and toward the right on the horizontal scale. The scale on both the X and Y-axes should be sufficient to include both the largest and the smallest X and Y values in the table. 3. Plot the data pairs on the diagram by placing a dot at the intersections of the X and Y co-ordinates for each data pair. 4. Interpret the scatter diagram for direction and strength

Interpreting The Direction: Data patterns may be positive, negative, or display no relationship. A positive relationship is indicated by an ellipse of points that slopes upward demonstrating that an increase in the cause variable also increases the effect variable. A negative relationship is indicated by an ellipse of points that slopes downward demonstrating that an increase in the cause variable results in a decrease in the effect variable. A diagram with a cluster of points such that it is difficult or impossible to determine whether the trend is upward sloping or downward sloping indicates that there is no relationship between the two variables. 10718243.doc

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Details on Seven QC Tools CQA Doc No 17

Interpreting The Strength: Data patterns, whether in a positive or negative direction, should also be interpreted for strength by examining the "tightness" of the clustered points. The more the points are clustered to look like a straight line the stronger the relationship. EXAMPLES

PARETO CHART A Pareto Chart is a special form of a bar graph and is used to display the relative importance of problems or conditions. A Pareto Chart Is Used For: 1. Focusing on critical issues by ranking them in terms of importance and frequency (example: Which course causes the most difficulty for students? which problem with Product X is most significant to our customers?) 2. Prioritising problems or causes to efficiently initiate problem solving (example: Which discipline problems should be tackled first? or, What is the most frequent complaint by parents regarding the school? solution of what production problem will improve quality most?) 3. Analysing problems or causes by different groupings of data (e.g., by program, by teacher, by school building; by machine, by team) 4. Analysing the before and after impact of changes made in a process (example: What is the most common complaint of parents before and after the new principal was hired? has the initiation of a quality improvement program reduced the number of defectives?) Steps In Constructing A Pareto Chart With Step-By-Step Example: 1. Determine the categories of problems or causes to be compared. Begin by organising the problems or causes into a narrowed down list of categories (usually 8 or less).

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Details on Seven QC Tools CQA Doc No 17 2. Select a Standard Unit of Measurement and the Time Period to be studied. It could be a measure of how often something occurs (defects, errors, cost overruns, etc.); frequencies of reasons cited in surveys as the cause of a certain problem; or a specific measurement of volume or size. The time period to be studied should be a reasonable length of time to collect the data. 3. Collect and summarise the Data. Create a three-column table with the headings of "error or problem category", "frequency", and "percent of total". In the "error or problem category" column list the categories of problems or causes previously identified. In the "frequency" column write in the totals for each of the categories over the designated period of time. In the "percent of total" column, divide each number in the "frequency" column by the total number of measurements. This will provide the percentage of the total. Error Category Frequency Percent of Total Punctuation Grammar Spelling Typing TOTAL

22 15 10 3 50

44% 30% 20% 6% 100%

4. Create the framework for the horizontal and vertical axes of the Pareto Chart. The horizontal axis will be the categories of problems or causes in descending order with the most frequently occurring category on the far left (or at the beginning of the horizontal line). There will be two vertical axes-one on the far left and one on the far right. The vertical axis on the far-left point will indicate the frequency for each of the categories. Scale it so the value at the top of the axis is slightly higher than the highest frequency number. The vertical axis on the far right will represent the percentage scale and should be scaled so that the point for the number of occurrences on the left matches with the corresponding percentage on the right. 5. Plot the bars on the Pareto Chart. Using a bar graph format, draw the corresponding bars in decreasing height from left to right using the frequency scale on the left vertical axis. To plot the cumulative percentage line, place a dot above each bar at a height corresponding to the scale on the right vertical axis. Then connect these dots from left to right, ending with the 100% point at the top of the right vertical axis. 6. Interpret the Pareto Chart. Use common sense-just because a certain problem occurs most often doesn't necessarily mean it demands your greatest attention. Investigate all angles to help solve problems-What makes the biggest difference? What will it cost to correct the problems? What will it cost if we don't correct this problem?

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Details on Seven QC Tools CQA Doc No 17

CAUSE AND EFFECT DIAGRAM (Fishbone Diagram) A Cause and Effect Diagram is an analysis tool to display possible causes of a specific problem or condition. A Cause And Effect Diagram Is Used For: 1. Identifying potential causes of a problem or issue in an orderly way (example: Why has membership in the band decreased? why isn't the phone being answered on time? why is the production process suddenly producing so many defects?) 2. Summarising major causes under four categories (e.g., People, Machines, Methods, and Materials or Policies, Procedures, People, and Plant) Steps In Constructing A Cause And Effect Diagram: 1. Prepare a flip chart or an overhead transparency of the following template:

1. Write the issue (problem or process condition) on the right side of the Cause and Effect Diagram. 2. Identify the major cause categories and write them in the four boxes on the Cause and Effect Diagram. You may summarise causes under categories such as: -Methods, Machines, Materials, People -Places, Procedures, People, Policies, -Surroundings, Suppliers, System, Skills 3. Brainstorm potential causes of the problem. As possible causes are provided, decide as a group where to place them on the Cause and Effect Diagram. It is acceptable to list a possible cause under more than one major cause category. 4. Review each major cause category. Circle the most likely causes on the diagram.

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Details on Seven QC Tools CQA Doc No 17 5. Review the causes that are circled and ask, "Why is this a cause?" Asking "why" will help get to the root cause of the problem. 6. Reach an agreement on the most probable cause(s). Example of Completed Cause/Effect Diagram:

CHECK SHEET The Check Sheet is a data-gathering and interpretation tool. A Check Sheet is used for: 1. Distinguishing between fact and opinion (example: how does the community perceive the effectiveness of the school in preparing students for the world of work?) 2. Gathering data about how often a problem is occurring (example: how often are students missing classes?) 3. Gathering data about the type of problem occurring (example: What is the most common type of word processing error created by the students-grammar, punctuation, transposing letters, etc.?) Steps to create a Check Sheet 1.

Clarify the measurement objectives. Ask questions such as "What is the problem?", "Why should data be collected?", "Who will use the information being collected?", "Who will collect the data?"

2. Create a form for collecting data. Determine the specific things that will be measured and write this down the left side of the check sheet. Determine the time or place being measured and white this across the top of the columns. 3. Collect the data for the items being measured. Record each occurrence directly on the Check Sheet as it happens. 4. Tally the data by totalling the number of occurrences for each category being measured.

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Details on Seven QC Tools CQA Doc No 17 AFFINITY DIAGRAM

An Affinity Diagram is a creative process, used with or by a group, to gather and organise ideas, opinions, issues, etc. An Affinity Diagram Is Used For: 1. Adding structure to a large or complicated issue (example: What are the issues relative to implementing a thematic approach to teaching?; what are the central issues in the development of a particular new product?) 2. Breaking down a complicated issue into broad categories (example: Which departments are more likely to implement TQM in this school?; what is the major steps in the completion of a complex project?) 3. Gaining agreement on an issue or situation (example: Which direction should the school take to restructure its curriculum?; how should a new product be marketed?) Steps In Constructing An Affinity Diagram: 1. State the issue or problem to be explored. Start with a clear statement of the problem or goal and provide a time limit for the session-usually 45-60 minutes is sufficient. 2. Brainstorm ideas for the issue or problem. Each participant should think of ideas and write them individually on index cards, sticky notes, or have a recorder write them on a flip chart. 3. Collect the cards or sticky notes, mix them up and spread them out (or stick them) on a flat surface (e.g., desk or wall). Index cards can easily be secured to a wall with a putty-type adhesive. 4. Arrange the cards or sticky notes into related groups. For approximately 15 minutes allow participants to pick out cards that list related ideas and set them aside until all cards are grouped. 5. Create a title or heading for each grouping that best describes the theme of each group of cards.

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