1
Graphical Descriptions of Data

2
Lessons
•
Frequency Distributions
•
Graphical Displays of Data: Pie Charts
and Bar Charts
•
Graphical Displays of Data: Histograms,
Polygons, Stem and Leaf Plots
•
Analyzing Graphs

3
Frequency Distributions

4
Objectives
•
Learn how to construct a frequency
distribution.
•
Know the characteristics of a frequency
distribution.

5
Introduction
•
After collecting data you need to organize it so
that inferences and conclusions can be made.
•
Raw data is not useful if you want to know the
lowest price or the average.

6
Introduction
•
If we create an
ordered array
then we can easily
see the lowest price and the highest price
•
Which price is common?
•
Is there a pattern to the data?

7
Constructing a Frequency
Distribution
•
A
distribution
displays data values that
occur and how frequently each value
occurs.
•
A
frequency distribution
is a table that
divides the data into groups, called
classes
, and shows how many data
values occur in each group.
•
The
frequency
,
f
, of a group, or class, is
the number of data values in that class.

8
Constructing a Frequency
Distribution
•
Ungrouped Frequency Distributions
–
A frequency distribution where each class
represents a single value.
–
Ideal when the data set is relatively small, or
contains only a few possible values.
–
E.g., the distribution of letter grades A, B, C,
D, F.

9
Constructing a Frequency
Distribution
•
Grouped Frequency Distribution
–
A frequency distribution where the classes are
ranges of possible values.
–
Ideal with large data sets containing many
different values for the variable.
–
E.g., if we used ungrouped frequency
distribution for our refrigerator example we
would have 20 classes. A grouped frequency
distribution will result in fewer classes hence
more manageable.

10
Constructing a Frequency
Distribution
Steps for Constructing a Frequency
Distribution
1.
Decide how many classes should be in
the distribution.
2.
Choose an appropriate class width.
3.
Find the class limits.
4.Determine the frequency of each class.

17

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- Fall '18
- F. TAILOKA
- Frequency, Frequency distribution, Bar chart, Histogram