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  • A graph consisting of a series of vertical columns, such that the area of each column represents observed frequencies in a class interval (also referred to as interval or bin).
  • Used to display the shape of a frequency distribution.
  • Particularly useful when there are a large number of observations.
  • A type of bar graph.
  • Also called histograph.

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Tip: When creating a histogram...
  • Leave no space between bars when the class intervals represent continuous data; bar graphs, drawn with a gap between bars, are used to represent discrete data (i.e., different categories).
  • Graph the observed frequency in each class interval (also called the class frequency) for datasets with a small to medium number of observations; label the y-axis "Frequency." Graph the relative frequency in each class interval for datasets with a large number of observations; label the y-axis "Proportion" or "Relative Frequency."


A typical histogram

Pulse rates, in beats per minute, were calculated for 192 students enrolled in a statistics course at the University of Adelaide.[1] The first step in creating a histogram is to create a frequency table.

Pulse Rate for a Sample of Students
from the University of Adelaide
Pulse Rate Count
(34-41] 2
(41-48] 2
(48-55] 4
(55-62] 19
(62-69] 40
(69-76] 53
(76-83] 30
(83-90] 27
(90-97] 10
(97-104] 5
Total 192

Using the class frequencies (the number of observations in each class interval) shown in the frequency table, the following histogram was created.[2]


Exploring the effect of class interval size

See West's histogram applet for an opportunity to experiment with different class interval sizes.


  1. See the dataset, survey, available in the MASS package in R, an open source statistical computing software application.
  2. Created in R using the command:
    hist(Pulse,breaks=c(34,41,48,55,62,69,76,83,90,97,104),xlab="Pulse, beats/min",main="Pulse Rate for a Sample of Students")