Wednesday, June 26, 2013
It is the intent of this course to teach the student the value of learning and applying methods of statistical process control for process improvement and encourage the student either to learn these methods via self-study or from a training course. Although it is not the intent to teach these methods in this course giving examples may help the student understand the value of learning and applying them. Therefore this lecture provides simple examples of process improvement methods and tools to enable the student to get a feel for what is involved in process improvement and begin using these methods on simple processes. The lecture is a bit long and requires careful reading because there are a number of important concepts involved and simpler examples would not adequately present these concepts. Read this lecture when you are fresh and can devote time for a tedious but important read.
The example presented here is a college library’s book search and checkout process. Let’s assume that the librarians are receiving complaints that it takes too long to find and check out books. Process improvement shouldn’t have to wait until customers make complaints but complaints can help direct the improvement process. When the librarians first decided that they were getting so many complaints that they should try to fix the problems the head librarian wasn’t convinced that the complaints reflected any real problems. She felt that there might be just a few disgruntled students complaining. Therefore they decided to collect some data over the next week. They used a check sheet to collect the data. Check sheets are used to collect numerical data over a period of time. A check is made on a form or any sheet of paper each time an event of interest is observed. The check sheet resulting from the librarians monitoring of the fraction of library users complaining about any of the library's processes is shown in figure 20.
Figure 20 Check sheet recording the complaints about library service for one week.
Seeing that complaints were being received from an average of 17% of the library’s users the head librarian authorized the librarians to form a process improvement team to try to improve the library’s processes so that complaints would be reduced.
Flowcharting to define the process
The first step for the process improvement team is to conduct a brainstorming meeting to discuss the complaints and plan how to react to the complaints. To help guide the brainstorming meeting the team prepared a flow chart of the library’s process for finding and checking out books. The team’s flow chart is shown in figure 21.
Figure 21 The process improvement team’s flow chart for the process of finding and checking a book out of a library.
A flow chart diagrammatically lists each step in a process in a time ordered sequence. Flow charts establish ownership of process steps, establish boundaries, define key interfaces and define the overall process and thereby ensure that the team has a common understanding of the process in question. Flow charts are most helpful for complex processes where there a lot of decision points, inspection points and loop backs. The charts help clarify what is really happening in a process vs. what might have been planned and the charts are an excellent tool for helping a process improvement team focus its discussion and brainstorming sessions.
There are useful variations on flow charts including listing items under columns labeled Supplier, Input, Process, Output and Customer in the sequence of the processes forming an overall process. Examining a process several times using different format charts often reveals new insights into the process. Perhaps you can think of even more ways to define the flow of processes in your organization.
Analyzing the process
The team discussed each step in the flow chart to get ideas for what might be the source of the students' complaints. At a brainstorming meeting each attendee is allowed to offer any ideas for the cause of the problems and any ideas for developing solutions. All ideas are recorded first, and then they are discussed to select those that are most promising. Constructing a cause and effect diagram, often called a fishbone diagram, is a good tool for collecting and discussing ideas for the causes of the complaints. A final fishbone diagram for the library’s slow process might look like that shown in figure 22. It helps guide the brainstorming if the possible causes of problem are grouped in four categories. Use the four P’s of Procedures (including Processes), People, Policies and Plant (i.e. buildings and equipment) for four categories of problems in service organizations. Similarly, the four M’s of Material, Methods, Machines, and Man are helpful categories of problems in manufacturing or project organizations that deal with things rather than services. Over time your organization may find other categories that are more useful for your specific organization. A category that is often added is Environment.
Figure 22 Fishbone diagram of potential causes for slow library process.
The next step is to gather data to determine which of the potential causes are the biggest contributors to the students’ complaints. Two approaches are to gather data from the students that are complaining and to gather data on the process itself. Data can be gathered from the students by querying them during checkout and/or by asking them to participate in a survey. Let’s assume the librarians decide to use a survey. They design the survey based on the data in the fishbone diagram. The result is the following list of questions:
1. Do you think finding and checking out a book is?
Too slow ____
2. Do you think the process is?
Too complex ____
If too complex, what part of the process do you find the most complex?__________________________________________
1. Are the library’s instructions helpful?___ , Little help?____, No help?_____
2. Are the librarians helpful?____, Little help?_____, No help_____?
3. Which step takes you the most time?
a. Finding desired books in the catalog______
b. Finding books in the stacks_______
c. Checking out the books you have found_______
4. What changes would improve the process for you? __________________________________________________________________________________________________
5. When you need help from a librarian is there usually one available? Yes__,No__
6. Is the library open when you need to get books? Yes____, No_____
Let’s assume that 100 surveys are collected and analyzed. The finding might look like the following: (Note numbers won’t add up as some students won’t answer all questions.)
1. Do you think finding and checking out a book is?
Too slow __85
2. Do you think the process is?
Too complex ____84
If too complex, what part of the process do you find the most complex? 65 said the having to give too much data to the librarians; 10 said finding books in the catalog and 4 said finding books in the stacks.
3. Are the library’s instructions helpful? __11, Little help? _73, No help? _8
4. Are the librarians helpful?__92, Little help?___6, No help___1?
5. Which step takes you the most time?
a. Finding desired books in the catalog___25
b. Finding books in the stacks_____40
c. Checking out the books you have found___32
6.What changes would improve the process for you?___74 said having to provide just student name or name and ID number to the checkout librarian, 10 said adding more catalog computers, 5 gave miscellaneous answers and 6 gave no answers.
7. When you need help from a librarian is there usually one available? Yes_87, No_10
8. Is the library open when you need to get books? Yes__86, No___12
It is clear from the results of the survey that the biggest source of complaints is having to give the student’s name, local address and home address each time a book is checked out, as required by the library’s policy and the checkout software. The students recommend having to provide only their name or their name and student ID number. The library is open when most students need it open and the librarians are available and helpful for most students. Similarly, finding books in the catalog and in the stacks take time but are not problems for most students.
The survey provides useful information but the librarians must analyze the process, implement candidate improvements and check the effectiveness of the candidate improvements. Analyzing the process means establishing measurement points, collecting data and checking the collected data to see if the actual time data correlates with the students’ complaints.
During the time the surveys were being collected an assistant librarian timed students as they performed the different tasks involved. These times were collected for 85 students. The total times were analyzed in 15 samples of 5 students each and the average total times of each sample of 5 were plotted in a control chart called an “X bar- R” chart. (There are mathematical reasons for working with averages of subgroups, which you will learn in your more comprehensive studies of statistical methods.) X-bar stands for the average of each sample group and R stands for the range in value of the sample. The resulting chart is shown in figure 23.
Figure 23 X bar-R chart for total process times for 15 sample groups of 5 students each.
The upper control limit is calculated from the equation UCL= X bar + 0.577R bar and the lower control limit from LCL= X bar- 0.577R bar. (The parameter 0.577 is specific to sample averages of 5 items per sample group and would be different if more or less than 5 items are in the sample group. Books on statistical process control, like the Memory Jogger, list the equations and parameters needed to develop control charts.)
The control chart in figure 23 tells the librarians that the overall process is stable, i.e. it exhibits only common cause variation. Therefore they can make changes to the process and be assured that changes in the average times are due to their changes and not something else going wrong. Had there been points above the UCL and/or below the LCL the process would have special cause variation and the effect of any changes couldn’t be reliably attributed to the change.
Knowing they have a stable overall process the process improvement team examined the average times of the various steps in the overall process. The results are shown in table provided in figure 24. Note that before making any changes to any step in the process it is necessary to examine the control chart for that step to ensure the step is stable as well as the overall process. For this example we assume each step is stable.
Figure 24 Table of average times for each step in finding and checking out a book
The timed process data provides further insight into the students’ complaints. They complain that the process is too slow and complex and they identify having to provide too much data to the checkout librarian as their biggest contributor to their complaints. The data suggests that having to supply the personal data is irritating rather than taking too much time. The largest contributor to the total average time is the time spent in the stacks and the students did not complain about this time.
A Pareto chart is a bar graph with the data ordered from left to right so that the largest is on the left, the second largest next, etc. This chart helps a process improvement team focus on the problem to solve first. Using the data table in figure 24 prepare a Pareto chart of the data. Your result should look like figure 25.
Figure 25 A Pareto chart for the times of each step in the overall process.
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