Seven Basic Quality Control Tools and Techniques | Quality Control
4) Flow Chart
- Run Charts
- Pareto Charts
- Flow Charts
- Scatter Diagrams
- Cause and Effect Diagrams
- Control Charts
A Histogram is a bar graph used to present frequency data. Histograms provide an easy way to evaluate the distribution of data over different categories
Steps in making Histogram
- Define Categories for Data
- Collect Data, sort them into the categories
- Count the Data for each category
- Draw the Diagram. Each category finds its place on the x-Axis.
- The bars will be as high as the value for the category
The histogram reveals the following about the process
- Centering of the process data: The centering of the data provides information on the process about some mean.
- Spread of the data: Histogram width defines the variability of the process about the mean
- Shape of the histogram: Bell or normal shaped histogram is expected. Other than normal or bell shape means something wrong with the process responsible for poor quality.
Limitations of the Histograms
- The randomness in the data in developing histogram losses the vital information
- As data are not represented in order, the time-dependent or time-related trends in the process may not be revealed.
2) Run Chart
Run Charts are better option over histograms as they overcome the limitations of the histograms. A run chart represents change in measurement over a sequence or time. Run charts are used to determine cyclic events and their average values.
Steps in making Run Charts
- Arrange data with time sequence
- Plot the data in order
- Interpreting Data
|Fig. Run Chart|
The run chart reveals the following about the process
- Run charts display process performance over time
- Trends, cycles, and large variations are clearly visible
- An average line may be added to a run chart to clarify movement of the data away from the process average
3) Pareto Chart
VILFREDO PARETO an Italian economist provided a golden rule which fits into many managerial situations. The golden rule he noticed is “WEALTH IS CONCENTRATED IN A FEW PEOPLE”. Pareto principle : “The majority of wealth is held by a disproportionately small segment of the population”. This principle is also known as 80 / 20 principle. 80% of the problems are caused by 20% of the causes
JURAN has noticed that this principle applies to quality improvement as well. According to Juran the problems that occur a few are very frequent while other important problems occur seldom. He given the phrase as “Vital few and the trivial many”
Pareto Charts are used to apply the 80/20 rule of Joseph Juran which states that 80% of the problems are the result of 20% of the problems. A Pareto Chart can be used to identify that 20% root causes of problem.A Perot chart is similar like histogram.
Steps in making Pareto Charts
A flow chart is way of representing a procedure using simple symbols and arrows. A Flow chart shows the activities in a process and the relationships between them. A Flow chart lets a process be understood easily. It also demonstrate the relationships between the elements of the process.
|Fig. Flow chart|
Steps in making Flow Charts
- Determine the Process need to be represented by flow chart
- List down the sequence of operation and other details
- Start at a certain point and go then step by step
- Using flow chart symbols
- Write the titles to each element
5) Scatter Diagram
Scatter diagram is a statistical chart which shows a trend in a series of data. It demonstrates correlations between values.
|Fig. Scatter Diagram|
Steps in making Scatter Diagram
- Plot the data points
- Draw trend line by fitting a straight line
- Upward line shows the positive trend(X increases and Y increases)
- Downward line shows the negative trend (X increases and Y decreases)
6) Cause and Effect Diagrams.
A Cause and Effect Diagram shows the relationship between effect and the categories of their causes. The diagram look like a fishbone it is therefore also called fish-bone diagram. Cause and effect diagram enables a team to focus on the content of a problem. It helps to provide a comprehensive picture of the problem and the root causes of the same.
|Fig. Cause and Effect Diagram|
Steps in making Cause and Effect Diagram
- Determine the Effect or Problem
- Categorize the possible causes
- Describe the possible causes
7) Control Chart
Control charts are statistical tool, showing whether a process is in control or not. It is a graphical tool for monitoring the activities of an ongoing process also referred as Shewhart control charts.
|Fig. Control Chart|
Steps in making control chart
- Define Upper limit, lower limit and Center line
- Draw Chart
- Plot the data points into chart
- Interpret the control chart