Biostatistics for Animal Science

2 Biostatistics for Animal Science
1.2 Graphical Presentation of Qualitative Data
When describing qualitative data each observation is assigned to a specific category. Data
are then described by the number of observations in each category or by the proportion of
the total number of observations. The frequency for a certain category is the number of
observations in that category. The relative frequency for a certain category is the proportion
of the total number of observations. Graphical presentations of qualitative variables can
include bar, column or pie-charts.
Example: The numbers of cows in Croatia under milk recording by breed are listed in the
following table:
Breed Number of cows Percentage
Simmental 62672 76%
Holstein-Friesian 15195 19%
Brown 3855 5%
Total 81722 100%
The number of cows can be presented using bars with each bar representing a breed
(Figure 1.1).
Breed
Brown
Holstein
Simmental
3855
15195
62672
0 20000 40000 60000 80000
Number of cows
Figure 1.1 Number of cows under milk recording by breed
The proportions or percentage of cows by breed can also be shown using a pie-chart
(Figure 1.2).