5.1 SIPOC, Box Whisker Plots, Cause and Effect Diagrams and Check Sheets

c. SIPOC

SIPOC stands for Suppliers-Inputs-Process-Outputs-Customers. SIPOC is a tool used to identify all elements of a process before the beginning of a project. It is a high level flowchart of a process and lists all suppliers, inputs, outputs and customers. It provides a quick bird’s eye view of the elements of a process. A SIPOC diagram is mostly employed in the Measure phase of the DMAIC methodology. 

SIPOC is a tool that helps to define the specific portion of the overall business process that is targeted for improvement. It is a method of applying mapping to sub processes until arriving at that part of the process allocated for improvement. It is often used at the start of the project, when the key elements of the project have to be defined. It is also used when information is not clear about what the process inputs and outputs are, and who the suppliers and customers are. 

Steps in creating a SIPOC diagram

1. Set up a working surface that will enable the team to post additions to the SIPOC diagram. This can be a flipchart, sticky notes posted to a wall or a transparency. 
2. Identify the process. Create a macro process map; map it into four or five high level steps. 
3. Identify all outputs of the process. Attach them on the working surface. 
4. Identify the customers who receive these outputs. Record them separately. 
5. Identify the inputs that the process needs for it to function properly. Again attach these separately. 
6. Identify the input’s suppliers. Again record them separately. 
7. Review the work to edit omissions, unclear phrases, duplications etc. 
8. Draw a complete SIPOC diagram.

d. Box Whisker Plots

A box and whisker plot is a graph that summarizes the most important statistical characteristics of a frequency distribution for easy understanding and comparison. (Nancy R. Tague, 2005) A box and whisker plot, also known simply as a box plot, looks like a box representing the central mass of the variation and has thin lines which extend out on either side, called whiskers, representing the spread of the distribution. The box plot is simple to construct but displays a good amount of information; therefore it is a potent tool. 

box plot is used when analyzing the most important information about a batch of data or when two or more sets of data have to be compared. It can also be used when data on some other graph, like control charts, have to be summarized. 

Steps in creating a box and whisker plot (Craig Gygi, Neil DeCarlo, Bruce Williams, 2005)

1. Rank the captured set of data measurements for the characteristic. Reorder the captured data from the least to the greatest values. Refer to the numbers as X 1……X n.

2. Find the median of the data. Median is the observation value in the ordered data where half the values are larger and half are smaller. If the number of observations (n) in the data is odd, the median will be (n+1)/2 th value. Median = X (n+1)/2 If the number of observations (n) is even, the median is the average of the two middle values i.e. n/2 th and (n/2 +1) th value.

3. Find the first quartile Q 1. The first quartile is the point in the ranked ordered sequence, where 25% of the observations fall below this value.

4. Find the third quartile Q 3 . This is the point in the ranked ordered sequence, where 75% of the observations fall below this value.

5. Find the greatest observation X max.

6. Find the lowest observation X min.

7. Create a horizontal line, representing the scale of measure for the characteristic. This scale could be minutes for time, number of defects in an inspected part, centimeters for length etc.

8. Construct the box. Draw a box spanning the first quartile Q 1 to the third quartile Q 3. Draw a vertical line in the box corresponding to the calculated median value.

9. Draw the whiskers. Draw two horizontal lines, one stretching out from Q 1 to the smallest observation X min, and another extending from Q 3 to the biggest observation X max.

10. Repeat Steps 1 through 9 for each additional characteristic to be plotted and compared against the same horizontal scale.

Box and whisker plots are used to compare two or more distributions. These may be before or after a process is viewed. For example, to find out if two or more variation distributions are same or different, a box plot can be created. From figure 26.a it can be seen that distribution Q has the lowest level. But it still overlaps the performance of distribution P, meaning that it may not be that different. But distribution R does not overlap with P and Q and has a much higher value. It also has a much broader spread to its variation.

e. Cause and Effect Diagrams

Any process improvement initiative entails fighting the causes of variation. There can be a huge number of causes for variations to a given problem. Dr. Ishikawa is credited for creating the cause and effect diagram, which is a tool that is used for brainstorming possible causes of a problem in a graphical (tree structured) format. 

It is also known as the Fishbone diagram and the Ishikawa Diagram . This technique is called fishbone diagram because it resembles the skeleton of the fish. A fishbone diagram helps in getting to the root cause of the problem. It consists of a fish head at one end of the diagram- which states the problem. Besides this fish head, there is a fish spine and there are bones attached to the spine. The bones attached to the spine state the reasons which are causing the problem. 

The fishbone diagram is employed for problem-solving by the team members. It is used to collect all the inputs (which are causing the problem) and to present them in graphical manner. The advantage of using a Fishbone diagram is that besides detecting the problem, it helps the team to focus on why the problem occurs. 

Procedure of implementing a fishbone diagram :

Define the problem: List down the exact problem, in detail. It should be stated in a box, called the fish head. After stating the problem, draw a horizontal line, across the box. 

Brainstorm the causes: Attach sliding lines, called the bones of the fish, to the fish spine. These bones will state the causes because of which the problem occurred. Write down as many possible causes as could be involved. The major categories typically involved are:

The 4 M’s: Methods, Machines, Materials, Manpower

The 4 P’s: Place, Procedure, People, Policies

The 4 S’s: Surroundings, Suppliers, Systems, Skills

Further brainstorm the ‘brainstormed’ causes: Sketch out the smaller lines coming out of the larger bones, which will depict the possible causes within each category that may be affecting the problem. This helps breaking down a complex problem into smaller problems. Repeat this step until there is no breaking down of a problem into a sub-problem. 

Analyze the fishbone diagram: Finally analyze the diagram and draw out results by measuring the root cause. 

Example: Suppose the MNC dealing in the home delivery of pizzas wants to find out the various causes that are leading to a fall in their customer base. They depict the problem graphically, by putting the problem and causes under the fishbone diagram. 

The following is the fishbone diagram, tailored to the “pizza home delivery” example:

In the fish head, the pizza problem has been defined. The main causes leading to the problem are defined under the fish bones. The causes are then further sub-classed into generic problems, like, one of the cause, which is “pizza not delivered in time”, has been further categorized into sub-causes, which infer the reasons why the pizza couldn’t be delivered in time. The reason could be any one of these: traffic congestion, the scooter’s tire was punctured or the pizza delivery boy couldn’t locate the address easily.

f. Check Sheets

A check sheet is a most common tool for collecting data. A check sheet is a structured form consisting of a list of items for collecting and analyzing data. It helps display the frequency of the data. It contains pre-recorded descriptions of events that are likely to occur. A well thought out check sheet consists of questions like: “Is everything done?” “How often does the problem occur?” “Have all inspections been performed?” 

Check sheets are tremendously useful for solving a problem and for process-improvement. Data collected in a check sheet can be used as inputs for other tools such as Pareto diagrams and histograms. They can be in the form of:

process check sheets where ranges of measurement values are written and actual observations are marked

defect check sheets where defects are described and frequencies are recorded

defect location check sheets which are actual diagrams that show where the problem occurs

cause and effect check sheets in which the problem area is shown by marking that area in the cause and effect diagram 

Steps in creating a check sheet 

1. Identify the problem to be observed. 
2. Decide when the data will be collected and what will be the duration 
3. Design the form such that data recorded does not have to be rewritten for analysis. For example, data can be recorded by simply making check marks or similar symbols against the fields 
4. Label all spaces on the form. 

Each time the targeted event takes place; record it on the check sheet. 

Example 1: The following table represents a defect check sheet in the delivery process of a pizza manufacturing chain.

Example 2: The following figure shows a check sheet used by HR to collect data on causes of increasing attrition rates in a BPO.

It is clear from the data collected that slow growth and high stress levels contributed to high attrition levels in one month. This data can be used for further analysis.

h. Stem and Leaf Plots

Stem and leaf plots are a quick way to examine the shape and spread of the data. It is a graphical method of displaying data. It is a type of histogram that displays individual data. 

Example: The following data shows the weights of male football players in the National Football League, 2005. 
143, 145, 149, 158, 159, 164, 167, 168, 167, 178, 170, 172, 178, 174, 180, 185, 194, 193, 192, 200, 209, 205, 203, 204, 206, 218, 215, 225, 228, 229, 226 

The following table shows a stem and leaf display of the data. To draw a stem and leaf display, first note that the data ranges from 140s to 220s, counting by tens. Note down a column of stems, starting with 14(representing the weights in 140s) and ending with 22(representing the weights in the 220s). Draw a vertical line separating the Stems, from the Leaves. The leaves represent the multiples of 1. 

The next step is to enter all raw scores into the stem and leaf display. A weight of 145 would be recorded by placing a 5 against the stem 14; a weight of 205 would be recorded by placing a 5 against the stem 20. Continue this process until all the data is plotted. The resulting display is like the shape of a histogram plotted by the same data.