Quality Control

What is Quality Control? Juran and Godfrey define Quality Control as “a managerial process for conducting operations so as to provide stability – to prevent adverse change and to “maintain the status quo” To maintain stability, quality control process includes the following: Evaluates actual performance Compares actual performance to goals Takes action on the differences Another definition: Operational techniques and activities used to fulfill quality requirements.

The difference between QC and QA Quality Control (QC) and Quality Assurance (QA) compare performance to goals. However !!!!!! In QC performance is evaluated during operations and performance is compared to goals during operations and the action is taken by the operating force. In QA performance is evaluated and compared after operations and resulting information is provided to operating forces and others who have needs to know.

The Feedback Loop 4- The process responds by restoring conformance 1- To evaluate the actual quality of the control subject 2- The umpire receives information from the sensor and compares them to the quality goals and standards 3- The actuator stimulates the process to change the performance to meet the standards Think of the thermostat to control temperature and the cruise control used in cars to control speed

A flowchart for the quality control process

The 7 Quality Control tools Check Sheets Scatter Diagrams Cause-and-Effect Diagrams Pareto Charts Flowcharts Histograms Control Charts

1- Check Sheets A check sheet is an organized method of recording data so that decisions can be based on facts rather than anecdotal evidence. Check Sheet items should be selected to be mutually exclusive and to cover all reasonable categories.

1- Check Sheets The following figure shows a check sheet used to determine the causes of defects in a hypothetical assembly process. If we had too many defects under the category “others”, a new set of categories is needed

2- Scatter Diagrams Scatter Diagrams show the relationship between two measurements. One measurement is plotted on the horizontal axis (x-axis) and the other is plotted on the vertical axis (y-axis). The distribution of their intersection points reveals the relationship pattern.

2- Scatter Diagrams The Coefficient of Correlation (r) is a measure of the strength of the relationship between two variables.

2- Scatter Diagrams The Correlation Coefficient r

2- Scatter Diagrams The sales manager of Copier Sales company wants to determine whether there is a relationship between the number of sales calls made in a month and the number of copiers sold that month. The manager selects a random sample of 10 representatives and determines the number of sales calls each representative made last month and the number of copiers sold.

2- Scatter Diagrams Does this mean that more sales calls cause more sales? No, we have not demonstrated cause and effect here, only that the two variables are related.

3- Cause-and-Effect Diagrams Known as the Fishbone charts and the Ishikawa diagrams Ishikawa diagrams are used to identify and understand the factors that are causing an undesired effect. The factors are identified by people who are familiar with the process involved. Contributing factors (Categories) could be the “four M’s”: Method, Manpower, Material, and Machinery or the “four P’s”: Policies, Procedures, People, and Plant. Individual causes associated with each categories are tied in a separate bones along that branch, often through a brainstorming process.

3- Cause-and-Effect Diagrams Contributing factors are not root causes. The team needs to examine the contributing factors to find the root causes. This can be done by digging deeper – asking repeated “why” questions of the contributing factors. Example: for a basketball quality control problem- missed free throws. Each bone represents a possible source of error (category or factor) The figure in the following slide showed that the Method category has problems caused by hand positions, follow-through, aiming point, bent knees, and balance. Further causes for the sub-branches can be developed and analyzed.

3- Cause-and-Effect Diagrams Material (ball) Method (shooting process) Size of ball Lopsidedness Grain/Feel (grip) Air pressure Follow-through Hand position Aiming point Bend knees Balance Missed free-throws Training Conditioning Motivation Concentration Consistency Manpower (shooter) Rim alignment Rim size Backboard stability Rim height Machine (hoop & backboard)

4- Pareto Charts Pareto charts are a method of organizing errors, problems, or defects to help focus on problem solving efforts. They are used to identify a set of priorities. They are based on the work of Vilfredo Pareto, a 19th-centory economist who noted that a few people controlled most of the nation’s wealth. Joseph Juran popularized Pareto’s work when he suggested that 80% of a firm’s problems are a result of only 20% of the causes. Separating the “vital few” from the “trivial many” can be done using the Pareto Charts.

4- Pareto Charts Using the data from the hypothetical assembly process

4- Pareto Charts Data for October 54 12 4 3 2 70 – 60 – 50 – 40 – 30 – 70 – 60 – 50 – 40 – 30 – 20 – 10 – 0 – Frequency (number) Causes and percent of the total Cumulative percent Data for October – 100 – 93 – 88 – 72 Room svc Check-in Pool hours Minibar Misc. 72% 16% 5% 4% 3% 12 4 3 2 54 Number of occurrences

5- Flowcharts Flowcharts graphically present a process or system using annotated boxes and interconnected lines. They are a simple but great tool for trying to make sense of a process or explain a process. Flowcharts should reflect the actual process used rather than what the process owner thinks it is or wants it to be. We can get a brief idea about the critical path of the process and the events involved in the critical path. Measurements could be taken at each step to find the significant causes of delays.

5- Flowcharts A hospital is undertaken a series of process improvement initiatives. One of these is to make the MRI service efficient for patients, doctors, and hospital. The first step is to develop a flowchart for this process Physician schedules MRI Patient taken to MRI Patient signs in Patient is prepped Technician carries out MRI Technician inspects film If unsatisfactory, repeat Patient taken back to room MRI read by radiologist MRI report transferred to physician Patient and physician discuss 9 8 80% 11 10 1 2 3 4 5 6 7 20%

6- Histograms Histograms show the range of values of a measurement and the frequency with which each value occurs. They show the most frequently occurring reading as well as the variations on the measurements. Descriptive statistics, such as the average and the standard deviation, may be calculated to describe the distribution. The visual presentation of the distribution may also provide insight into the cause of variation.

6- Histograms Example Another example could be the time spent to take a blood sample. If the intended average is in the middle and the variation is not that high then thing could be accepted.

For the same group distribution Assignment 2 For the same group distribution Each group is asked to do the following Find a real time problem at work and use the cause-and-effect diagrams to find the causes of the problem. (please explain the problem clearly in one slide) Use a large set of data (greater that 500 entity) then use one of the following tools to explain the data and find any interesting remarks (Scatter Diagrams, Pareto Charts, or Histograms) Prepare a ppt presentation to share your findings with your classmates next week. (I expect to receive your ppt slides and the data file at 11:30 am of the day of the lecture)