Organizing Data
(Frequency Tables and Histograms)
Once we have identified our objects of interest, specified the variable we wish to measure or observe, and collected our
data using an appropriate sampling method, it is then time to organize and display our data.
If we are working with a large set of quantitative data, a frequency table and histogram are a good way to organize and
display the data.
A frequency table allows us to place the data into smaller intervals or “classes” and the histogram will
allow us to make comparisons among these classes.
Histograms are much like bar chart, except a histogram is based on
intervals.
We are going to create a frequency table, find the relative frequency of each class and then use the organized data to
create a histogram in order to display the data.
Our frequency table will contain six columns: Class Limits, Class
Boundaries, Tally, Frequency, Class Midpoint, and Relative Frequency.
Not all frequency tables must contain all six of
these columns, but we’ll do our first one this way to help us stay organized as we go along.
Class Limits
Class
Boundaries
Tally
Frequency
Class
Midpoint
Relative
Frequency
Before we
define the class
limits, we must
determine the
class width.
This is the size
of the interval
we will use.
The class
limits
indicate the
lowest and
highest value
that can fit into
the class.
There is a
space between
the upper limit
of one class
and the lower
limit of the
next class.
The
½ way point is
called the class
boundaries.
Tally marks
are made each
time a data
value lands
within the class
limits.
The frequency
is the total
number of
tallies or the
total number of
data values
within the class
limits.
The midpoint
is the average
of the lower
and upper class
limit.
Lower + upper
2
This column
represents the
frequency of
each class
compared to
the total of all
frequencies.
It
is found by
dividing the
class frequency
by the total
number of data
values.
(
f/n
)
We’ll use the class limits and the frequency or relative frequency to create a histogram to display our data after creating
the frequency table to organize the data.
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 Spring '10
 me
 Frequency, Interest, Frequency distribution, Histogram, 23%, 30 Day

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