Table of Contents

Seven Basic Quality Control Tools and Techniques | Quality Control

Histograms
Run Charts
Pareto Charts
Flow Charts
Scatter Diagrams
Cause and Effect Diagrams
Control Charts

1) Histograms

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

Fig. Histogram

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

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

First define categories
Sort the data into the Categories and find out the
frequency of occurrence of each category
Arrange the categories in descending order

4) Flow Chart

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.

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.

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.

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.