Histograms: A
Valuable Tool for
Quality Evaluation
By Perry Katz
6/29/2016
1
Overview
1) What is a Histogram?
2) What are some possible uses
for a Histogram?
3) Where did the Histogram come
from?
4) How do Histograms work?
5) A real world example.
6) An exercise.
6/29/2016
2
What is a Histogram?
• A Histogram is a variation of a
bar chart in which data values
are grouped together and put
into different classes.
• This grouping allows you see
how frequently data in each
class occur in the data set.
6/29/2016
3
What is a Histogram
(cont.)
• Higher bars represent more data
values in a class.
• Lower bars represent fewer data
values in a class.
• On the next slide is an example
of what a Histogram looks like.
6/29/2016
4
Example of a Histogram
6/29/2016
5
Uses for a Histogram
A Histogram can be used:
• to display large amounts of data
values in a relatively simple chart
form.
• to tell relative frequency of
occurrence.
• to easily see the distribution of the
data.
• to see if there is variation in the
data.
• to make future predictions based on
6/29/2016
6
the data.
Where did the
Histogram Come From?
• The Histogram was first
implemented by Kaoru Isikawa,
one of Japans’ most renowned
experts on quality improvement.
• Isikawa spent his life trying to
improve quality in Japan.
6/29/2016
7
Histogram Come From?
(cont.)
• His major contributions to
quality improvement are known
as the basic seven tools of
quality.
• Included in his basic seven tools
of quality is the Histogram.
6/29/2016
8
How do Histograms
Work?
• First, you need need to pick a
process to analyze.
• Next, you need a large amount of
data, at least 100 data values so that
patterns can become visible.
• Then, you need to assemble a table
of the data values that you collected
with regards to frequency of data
values.
6/29/2016
9
How do Histograms
Work? (cont)
• Next, you need to calculate some
statistics for the Histogram,
including: mean, minimum,
maximum, standard deviation, class
width, number of classes, skewness,
and kurtosis.
• Then, you actually create the
Histogram using these statistics.
6/29/2016
10
How do Histograms
Work? (cont)
• After you have created a
Histogram, it will take one of
five shapes:
• Normal Distribution:
6/29/2016
11
How do Histograms
Work? (cont)
• Positively Skewed:
• Negatively Skewed:
6/29/2016
12
How do Histograms
Work? (cont)
• Bi-Modal Distribution:
• Multi-Modal Distribution:
6/29/2016
13
How do Histograms
Work? (cont)
• Once your Histogram is
complete, you can analyze its
shape, as well as the statistics
that you came up with.
• This analysis will help you to
make better decisions toward
quality improvements.
6/29/2016
14
Real World Example
• The next slide contains a real world
example of a histogram. It plots the
relative frequency of the heights of
some students based on the data
below.
Height (feet):
0-2
2-4
4-5
5-6
6-8
6/29/2016
Frequency:
(Number of pupils) Relative frequency:
0
0
1
1
4
8
8
16
2
2
15
Real World Example
•
This Histogram is courtesy of http://www.gcsemaths.fsnet.co.uk/page5.html
6/29/2016
16
Exercise
• A great exercise which would help
you better understand what a
histogram is all about can be found
at :
http://www.usfca.edu/histogram_explorer/he.html
Here you are walked through the
making of a histogram. You see all
of the aspects that I have discussed
in this tutorial.
6/29/2016
17
Summary
• After going through this
tutorial you should have a
better idea of:
1) What a Histogram is.
2) What a Histogram is used for.
3) Where the Histogram came
from.
4) How Histograms work.
6/29/2016
18
Histograms: A
Valuable Tool for
Quality Evaluation
By Perry Katz
6/29/2016
19