7 QC tools of quality

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Quality is what quality does. Quality is the characteristics of a product or service that bear on its ability to satisfy stated or implied needs with minimum variation or defects. In other words, it is a standard against which we measure the actual performance with no or minimum variation.

There are 7 basic tools of quality. The goal is to streamline quality control in manufacturing or business processes so there is little to no variance throughout.  

The quality tools of Six Sigma are as follows.

1.Cause & Effect: Cause and effect is also known as Ishikawa or fishbone diagrams. It is a graphical tool that helps identify, sort and display the possible cause of a problem.

 It is called “ Ishika Diagram” because it was invented by Kaaru Ishikawa. The other name of Cause and effect is Fishbone because it looks like the structure of a fishbone.

Common uses of the Ishikawa diagram are product design and quality defect prevention to identify potential factors causing an overall effect. Each cause or reason for imperfection is a source of variation. Causes are usually grouped into major categories to identify and classify these sources of variation.

2. Control Chart: Control chart is a generic tool that can be adapted for a wide variety of purposes. It is a graphical tool for monitoring changes that occurs within a process, by distinguishing variation that is inherent in the process (Common Cause) from variation that yields a change to the process ( Special Cause). 

This change may be a single point or a series of points in time- each is signal that something is different from what was previously observed and measured.

3. Check Sheet:  Check Sheet is a structured, prepared form for collecting and analysing data. It is a generic tool that can be adapted for a wide variety of purposes. 

The check sheet is 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.

4. Histogram: Histogram is the most commonly used graph for showing frequency distributions, or how often each different value in a set of data occurs. A histogram is an approximate representation of the distribution of numerical data. It was first introduced by Karl Pearson.

 To construct a histogram, the first step is to “bin” (or “bucket”) the range of values—that is, divide the entire range of values into a series of intervals—and then count how many values fall into each interval. The bins are usually specified as consecutive, non-overlapping intervals of a variable. The bins (intervals) must be adjacent, and are often (but not required to be) of equal size

5. Pareto chart: Pareto Chart is one of the most important tools of quality and is widely being used by almost all the organisations. Pareto chart is a bar graph that shows which factors are more significant. Pareto chart is a type of chart that contains both bars and a line graph, where individual values are represented in descending order by bars, and the cumulative total is represented by the line. The chart is named for the Pareto principle, which, in turn, derives its name from Vilfredo Pareto, a noted Italian economist.

The purpose of the Pareto chart is to highlight the most important among a (typically large) set of factors. In quality control, it often represents the most common sources of defects, the highest occurring type of defect, or the most frequent reasons for the customer complaints, and so on. Wilkinson (2006) devised an algorithm for producing statistically based acceptance limits (similar to confidence intervals) for each bar in the Pareto chart.

6. Scatter Plot: A Scatter plot is a basic graphic tool that illustrates the relationship between two variables. Scatter plot is a type of plot or mathematical diagram using Cartesian coordinates to display values for typically two variables for a set of data.

 If the points are coded (colour/shape/size), one additional variable can be displayed. The data are displayed as a collection of points, each having the value of one variable determining the position on the horizontal axis and the value of the other variable determining the position on the vertical axis.

7. Stratification: A technique that separates data gathered from a variety of sources so that patterns can be seen (some lists replace stratification with a flowchart or run chart). 

Stratification is defined as the act of sorting data, people, and objects into distinct groups or layers. It is a technique used in combination with other data analysis tools. When data from a variety of sources or categories have been lumped together, the meaning of the data can be difficult to see. This data collection and analysis technique separates the data so that patterns can be seen. 

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