The term experiment is defined as the systematic procedure carried out under controlled conditions in order to discover an unknown effect, to test or establish a hypothesis, or to illustrate a known effect. When analyzing a process, experiments are often used to evaluate which process inputs have a significant impact on the process output, and what the target level of those inputs should be to achieve a desired result (output). Experiments can be designed in many different ways to collect this information. Design of Experiments (DOE) is also referred to as Designed Experiments or Experimental Design - all of the terms have the same meaning.
Experimental design can be used at the point of greatest leverage to reduce design costs by speeding up the design process, reducing late engineering design changes, and reducing product material and labor complexity. Designed Experiments are also powerful tools to achieve manufacturing cost savings by minimizing process variation and reducing rework, scrap, and the need for inspection.
Components of Experimental Design
Consider the following diagram of a cake-baking process (Figure 1). There are three aspects of the process that are analyzed by a designed experiment:
Factors, or inputs to the process. Factors can be classified as either controllable or uncontrollable variables. In this case, the controllable factors are the ingredients for the cake and the oven that the cake is baked in. The controllable variables will be referred to throughout the material as factors. Note that the ingredients list was shortened for this example - there could be many other ingredients that have a significant bearing on the end result (oil, water, flavoring, etc). Likewise, there could be other types of factors, such as the mixing method or tools, the sequence of mixing, or even the people involved. People are generally considered a Noise Factor (see the glossary) - an uncontrollable factor that causes variability under normal operating conditions, but we can control it during the experiment using blocking and randomization. Potential factors can be categorized using the Fishbone Chart (Cause & Effect Diagram) available from the Toolbox.
Levels, or settings of each factor in the study. Examples include the oven temperature setting and the particular amounts of sugar, flour, and eggs chosen for evaluation.
Response, or output of the experiment. In the case of cake baking, the taste, consistency, and appearance of the cake are measurable outcomes potentially influenced by the factors and their respective levels. Experimenters often desire to avoid optimizing the process for one response at the expense of another. For this reason, important outcomes are measured and analyzed to determine the factors and their settings that will provide the best overall outcome for the critical-to-quality characteristics - both measurable variables and attributes that can be assessed.
Purpose of Experimentation
Designed experiments have many potential uses in improving processes and products, including:
Comparing Alternatives. In the case of our cake-baking example, we might want to compare the results from two different types of flour. If it turned out that the flour from different vendors was not significant, we could select the lowest-cost vendor. If flour were significant, then we would select the best flour. The experiment(s) should allow us to make an informed decision that evaluates both quality and cost.
Identifying the Significant Inputs (Factors) Affecting an Output (Response) - separating the vital few from the trivial many. We might ask a question: "What are the significant factors beyond flour, eggs, sugar and baking?"
Achieving an Optimal Process Output (Response). "What are the necessary factors, and what are the levels of those factors, to achieve the exact taste and consistency of Mom's chocolate cake?
Reducing Variability. "Can the recipe be changed so it is more likely to always come out the same?"
Minimizing, Maximizing, or Targeting an Output (Response). "How can the cake be made as moist as possible without disintegrating?"
Improving process or product "Robustness" - fitness for use under varying conditions. "Can the factors and their levels (recipe) be modified so the cake will come out nearly the same no matter what type of oven is used?"
Balancing Trade offs when there are multiple Critical to Quality Characteristics (CTQC's) that require optimization. "How do you produce the best tasting cake with the simplest recipe (least number of ingredients) and shortest baking time?"
Benchmarking is the process of comparing one's business processes and performance metrics to industry bests or best practices from other industries. Dimensions typically measured are quality, time and cost. In the process of best practice benchmarking, management identifies the best firms in their industry, or in another industry where similar processes exist, and compares the results and processes of those studied (the "targets") to one's own results and processes. In this way, they learn how well the targets perform and, more importantly, the business processes that explain why these firms are successful.
What is Benchmarking
Benchmarking is the process of determining who is the very best, who sets the standard, and what that standard is. In baseball, you could argue that seven consecutive World Series Championships made the New York Yankees the benchmark.
Once we decide what to benchmark, and how to measure it, the object is to figure out how the winner got to be the best and determine what we have to do to get there.
he check sheet is a form (document) used to collect data in real time at the location where the data is generated. The data it captures can be quantitative or qualitative. When the information is quantitative, the check sheet is sometimes called a tally sheet.[1]
Kaoru Ishikawa identified five uses for check sheets in quality control:[3]
To check the shape of the probability distribution of a process
To quantify defects by type
To quantify defects by location
To quantify defects by cause (machine, worker)
To keep track of the completion of steps in a multistep procedure (in other words, as a checklist)
A Check Sheet is a tool to collect both qualitative and quantitative facts about quality problems. When it is used to collect quantitative data, then known as tally sheet
“A tally sheet that can be used as a checklist when gathering data”
This is an effective tool from one of the 7 basic quality tools, both to prevent and detect problems by having structured valuable data about quality problems.
Differentiating with check list:
Some professional’s gets confused in check sheet and checklist. Check sheet is not a check list, checklist is basically listing of items need to be considered for the purpose of accuracy and completeness.
For example, maintaining a daily to-do task list is a good example of checklist while the check sheet is a collection of facts about a problem categorized by their cause, types, and/or location
Following table further explains the difference between check sheet and checklist:
Check Sheet
Check List
Check sheet conveys information about frequency of problems by type, causes and/or location
The Checklist is used to include all the necessary steps need to follow to ensure the accuracy and completeness of a work product or process. The Checklist can be used while working on a check sheet to ensure its accuracy. For example, what steps need to follow to develop check sheet while collecting real time data
It is normally developed and agreed by the team members as per need of the project. For example sometimes team chooses to develop it to count the frequency for the source of the problem, alternatively team can choose to capture frequency of the data categorised by causes. In other words, check sheet is customized by a team.
For a process, Checklist structure generally comes from the documented standards. Another checklist like to-do list comes from other influences, like someone is preparing to-do list as per expectations set.
These is a tool to record facts about interruptions or problems as a result of a quality control process
This is a tool to record what steps are required to fulfil an objective.
Where It Is Used?
Check sheet is one of the tools from 7 basic quality tools, and used in “Plan Quality” and “Control Quality as a Tool & Technique. Here, my basic objective is to explain the check sheet in the context of these two processes.
While planning a project, past projects document records are used as an input to identify the process improvements to know where sources and causes of defects encountered and where we may need to do efforts to prevent them in the current project. For example, we are using the same team which was involved in the previous project, these factual data can help us to identify how they are collectively executing a process and at what point we can prevent defects in work products.
Like past projects check sheet shows that many defects encountered under category of “misinterpretation of customer requirements” then we may result in a process improvement plan for “Collect Requirements” process. In addition, quality policies in quality management plan and metrics can be designed to measure future work performance and processes.
Check sheet is used as a Tool & Technique in “Control quality process to know about frequencies of problem in a format agreed by the team.
Example Check Sheet
In order to understand the concept I am taking an example that may be used in software project, here I am choosing to show the check sheet in terms of frequencies of quality problems categorized by their causes.
A test team member is evaluating work products to detect problems from the specifications. The team may choose to categorize data about quality problems in following categories:
Categories suggested by Roger S. Pressman:
Incomplete or erroneous specification (IES)
Misinterpretation of customer communication (MCC)
Intentional deviation from specifications (IDS)
Violations of programming standards. (VPS)
Error in data representations (EDR)
Inconsistent component interface (ICI)
Error in design logic (EDL)
Incomplete or erroneous testing (IET)
Inaccurate or inconsistent documentation (IID)
Error in programming language translation of design (PLT)
Ambiguous or inconsistent human/computer interface (HCI)
Miscellaneous (MIS)
While examination of work product test team member, team member assesses the defects and enter the frequencies in their respective category of causes like:
Check Sheet suggested by Roger S. Pressman in software engineering a practitioner’s approach:
Benefits of Check Sheet
Main objective of check sheet is to produce quantitative data about quality problems and use as an input of other seven quality tools like Histogram and Pareto analysis that will be discussed in my upcoming articles.
In addition check sheet is also used to collect qualitative data like no of interruptions that comes from intuition, judgement and feeling of observer.
In short it is an effective tool to collect both quantitative and qualitative data about quality problems.
The Check Sheet is a simple document that is used for collecting data in real time and at the location where the data is generated. The document is typically a blank form that is designed for the quick, easy, and efficient recording of the desired information, which can be either quantitative or qualitative. When the information is quantitative, the check sheet is sometimes called a tally sheet. The check sheet is one of the seven basic tools of quality control made popular by Dr. Kaoru Ishikawa.
Check Sheet used for Plan Quality Management purpose:
While planning a project, past projects document records are used as an input to identify the process improvements to know where sources and causes of defects encountered and where we may need to do efforts to prevent them in the current project. For example, we are using the same team which was involved in the previous project, these factual data can help us to identify how they are collectively executing a process and at what point we can prevent defects in work products.
Like past projects check sheet shows that many defects encountered under category of “misinterpretation of customer requirements” then we may result in a process improvement plan for “Collect Requirements” process. In addition, quality policies in quality management plan and metrics can be designed to measure future work performance and processes.
Check Sheet used for Control Quality purpose:
Check sheet is used as a Tool & Technique in “Control quality process to know about frequencies of problem in a format agreed by the team.
A defining characteristic of a check sheet is that data is recorded by making marks (“checks”) on it. A typical check sheet is divided into regions, and marks made in different regions have different significance. Data is read by observing the location and number of marks on the sheet. Four basic types of check sheets include:
Classification check sheet: A trait such as a defect must be classified into a category. If you just kept track of the total defects, you would know that you had 101 total defects. That is somewhat useful but that, in and of itself, does not provide much insight as to which day is the worst day or which source of defects is in the worst shape, etc. With a classification check sheet, it provides a visual overview of the problem areas.
Defect location check sheet: The physical location of a trait is indicated on a picture, or illustration of a part or item being evaluated. Instead of just keeping track of the number of defects, the defect location check sheet can sometimes reveal an area of the product that tends to see most of the defects. Once this is known, the team can go back to the process to see what it is about the upper right-hand corner of the product that is causing the defects.
Frequency check sheet: The presence or absence of a trait or combination of traits is indicated. Also, number of occurrences of a trait on a part can be indicated. Notice that if you just tracked the number of defects, you may not realize that Wrong Color has the highest frequency of occurrence. Furthermore, if Wrong Color was not broken down further, you might not realize that GREEN is giving you the most defects.
Measurement scale check sheet: A measurement scale is divided into intervals and measurements are indicated by checking an appropriate interval.
