Six sigma is comprehensive and flexible system for achieving, sustaining and maximizing business success. Six sigma is uniquely driven by close understanding of customer needs, disciplined use of facts, data and statistical analysis and diligent attention to managing, improving and reinventing business process.For years six sigma has been a popular management philosophy. In 1980s Motorola first made six sigma popular. AlliedSignal embraced it in the early 1990s and then General Electric made it the most popular management philosophy in history. All of six sigma begins with one equation Y= f(X) + e also called determinism. In this expression Y=f(X) +e:Y stands for outcome or results of a process. F stands for a transformation process. X stands for input variables of the process. E represents the error or potential for variation in each process.In simple language if we have X input and transform it with process we will get Y outcome. No matter how hard we try there will be degree of uncertainty or variation in the outcome, those variation is represented by Greek letter Epsilon or e.All outcomes are the result of inputs and process that acts on them, plus the error that creates variation. A process simply operates on the inputs to give us outcomes and its the fundamental action in changing from one condition to another, in making improvement, in adding value for our customers and our company. By looking behind carefully every output and examining the inputs, the process and the error that combined to produce it, we can try to understand what cause outcome. After we know the cause form next time we can control the outcome. First step to control outcomes is to understand to root cause. Many organization and companies want to improve their performance. They all know that their performance result are the outcome of all their business and work processes. So in order to improve their outcomes the organization and company has to change the way they do business. By changing processes, the function and combining the business inputs they can produce a better outcome. Determinism is the principle that we can create a desired outcome by configuring and controlling the inputs in a specific manner. In six sigma we can achieve our objective by analyzing the inputs, the process and the variation, and then implementing the best possible combination. By doing so we are directly controlling our environment rather than allowing environment controlling us.More we understand the relationship between inputs and outputs the better we can predict, determine and control the results.

Of all the issues that an engineer has to resolve, dealing with variation is the most difficult. (Davies, Ford)All variation is caused by something, if we have to control the outcome, we have to control the cause. If we have to control variation we have to understand whats causing it.There are two source of variation i. Common Cause Variation Common Cause variation is created by many factors that are commonly part of the process, and are acting totally at random and independent of each other. Their origin can usually be traced to the key elements of the system in which the process operates. (Materials, Equipment, People, Environment, Methods). If only common causes of variation are present, the output of a process forms a distribution that is stable over time.ii. Special Cause VariationSpecial Cause variation is created by a non-random event leading to an unexpected change in the process output. The effects are intermittent and unpredictable. These special causes are specific things we can identify and do something about.Its always best to work on reducing special cause variation before trying to reduce common cause variation because the process is not stable or predictable in special cause variation and we cant be sure of what is happening. But after eliminating special cause variation out of system we can then only improve its common cause variation.

Principle of measurement is one of the fundamental tenets of six sigma. We may work hard and even bring significant resources to a performance problem or improvement goal, but without measuring Ys and Xs, our ability to improve will only be meager and unsatisfactory. Taking measurements is a matter of using information and data to quantify the relationship between inputs, outputs and error in a given system, process or operating model. Measurement is the practice of collecting the data that relates to the inputs (X) and the given outcome (Y) which results from our process function f. Measurement enables us to gain a quantitative grasp on the characteristics of our various inputs and how they relate to our desired outcome. Measuring the inputs gives us profile of the way our process is playing out relative to a goal. Let say there is a guy name A his goal is to save Rs 5000 in a month Ys= Rs 5000, he works hard each day to achieve his goal but he kept spending on taxes, petrol, foods, necessities comes under Xs. In order to achieve his goal he has to start measure and control the performance of the Xs, he can spend less or earn more.Measuring Ys and Xs is first step towards greater efficiency and effectiveness. Its first step toward citizenship in the six sigma world of data oriented thinking.

Leverage means the ability to apply the critical few Xs that have the greatest impact on our desired Y in six sigma terms. We have to expend a little effort to find leverage when we do so it help us to overcome our problems and through the obstacles that stand between us and our goal. In creating any desired outcome vast majority of leverage surprisingly comes from small number of contributors. It applies in both simplest of goals as well as for the most complex systems. By finding those few critical inputs that give us leverage we can improve the outcomes. These vital few enable us to move the boulders in our life, our process or our organization.The law of the critical few versus the trivial many comes from the work of early 20th century Italian sociologist and economist Vilfredo Pareto. We may also know this law as the 80-20 rule where 20 percent of the inputs in any system account for 80 percent of the influence on that system. He determined mathematically that although many factors are connected to a given outcome, only a few carry the weight to change that outcome in a significant way. In a process, a few key variables are the cause of most problems or defects. This holds true even when you analyze the impact of dozens of variables involved in assemblies with hundreds of separate parts. When you look for leverage in business, you search for the minority of variables that provide the majority of power in solving problems in manufacturing, assembly, distribution, procurement, accounting, finance, customer service, so on.Leverage may not exist where we think it does its similar to illusion of cause and effect, we have to look closely, apply tests and challenge our assumptions to find true source of leverage. Factors that represent leverage in one situation may not represent leverage in another situation. Each process has its own unique dynamics and interactions.