INTRODUCTION Diagrams are particularly effective as a way of
conveying quite complex information. Presenting information
visually is easy to understand, and enables broad distributions and
trends to be taken in quickly.
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GRAPHICAL REPRESENTA TION OF FREQUENCY DISTRIBUTIONS Tabulated
frequency distributions are sometimes more readily understood if
represented by a diagram. Graphs and charts are normally much
superior to tables (especially lengthy complex tables) for showing
general states and trends. The methods of presenting frequency
distributions graphically are as follows: Frequency dot diagram
Frequency bar chart Frequency polygon Histogram Ogive. Stem and
leaf diagram
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Frequency Dot Diagram This is a simple form of graphical
representation for the frequency distribution of a discrete
variable.
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Frequency Bar Chart
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Frequency Polygon
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Histogram
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The Ogive This is the name given to the graph of the cumulative
frequency. It can be drawn in either the "less than" or the "or
more" form, but the "less than" form is the usual one
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Stem and Leaf Diagram In addition to providing a visual
representation of the data, stem and leaf diagrams can also allow
further analysis of the data as it is possible to obtain the
original data points from the diagram (i.e. there is no loss of
information). Similar to the histogram, a stem and leaf diagram is
a way of grouping your original data into classes. Like the
histogram, it provides a partial sorting of the original data to
allow a visual identification of the distribution pattern of the
data. Unlike the histogram, it provides extra detail regarding
individual values. In a stem and leaf diagram, each data value is
split into a stem and a leaf. The leaf is usually the last digit of
the number and the other digits to the left of the leaf form the
stem. The stem and leaf diagram is plotted by listing the first
digits (i.e. the "stems") in a column (and sorted in numerical
order), then listing the second digit (i.e. the "leaves") in a
second column to the right of the appropriate "stem" (and again
sorted in numerical order).
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Separate each number into a stem and a leaf. Since these are
two digit numbers, the tens digit is the stem and the units digit
is the leaf (e.g. for the number 79, the stem is "7" and the leaf
is "9") Next, group the numbers with the same stems (e.g. 79 and 77
are in the same group as both have a stem of 7). Then, list the
stems in numerical order (in our example, the stems range from 5 to
8 as the lowest value is 50 and the highest value is 87) in a
column.
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In a second column list the leaves to the right of the
appropriate stem values. If your leaf values are not in increasing
order, order them now. Finally, add a title to your diagram
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PICTOGRAMS Pictograms are the simplest method of presenting
information visually. These diagrams are variously called
"pictograms", "ideograms", or "picturegrams.
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PIE CHARTS Pie charts, known also as circular diagrams, are
used to show the manner in which various components add up to a
total. Like pictograms, they are only used to display very simple
information to non-expert readers.
