Frequency Distributions

Biostatistics BI 45, Saint Anselm College


Types of Frequency Distributions

Use - explorations and display of Data, Part of Exploratory Data Analysis (EDA), search for trends in data

Definition - used to count the frequency of occurrence of each datum in a sample of population

Methods of Displaying Results

Tables - simple listing of data

Bird Species Numbers
American Robins 43
House Finch 15

Charts or Graphs - many different options depending on variable - see below

Types of Charts or Graphs

Typical construction for most types of charts

Frequency on the y-axis and variable's values on the x-axis

Frequency Polygon - line graph

Bar Chart - for discrete measurements

Histogram - for continuous measurements, uses intervals

Pie Chart - used for relative frequency analyses, uses percentages

Stacked Graph - a relative frequency analysis that uses a bar chart


Minimal requirements needed to create a professional looking chart

Frequency Polygon, Bar Chart, Histogram, Stacked Graph

values on the x -axis, frequencies on the y - axis (see example below)

1 April, 15 April, 1 May, .......

labels identifying the variable on the x-axis (see example below)


label for y-axis (Frequency or Number of ....) (see example below)

Number of Sporadic Cases

legend with symbols used in graph (see example below)

not applicable for this graph


Bar Chart of Cyclosporiasis Outbreak of 1996

Pie Chart

Labels for Slices


Values and or % for slices

43, 42,6%


Contraceptive Use by New Jersey College Students

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Trademark and Disclaimers

Copyright © 2001 Jay Pitocchelli. All rights reserved. The contents of this page are the intellectual property of Dr. Jay Pitocchelli for distribution to students enrolled in Biostatistics BI 45 at Saint Anselm College. These pages may not be copied, photocopied, reproduced, translated, or published in any electronic or machine-readable form in whole or in part without prior written approval of Jay Pitocchelli. Students enrolled in Biostatistics BI 45 at Saint Anselm College have permission to print this material for their lecture notes. All formulae and critical values from: Zar, J. H. 1999. Biostatistical Analysis. (4th ed.). New Jersey, Prentice Hall.