Figure 17-4. Average Linear Velocity Histograms for E. Vernalis in 
Polarized Light and in Unpolarized Light 
NOTE: Dashed lines denote the estimated mean of each distribution. 
We have made special provision within the Bugsystem for the manipulation 
and statistical analysis of angular data. For example, the command 
*STAT/ AN/FI BUGS.DI BUGS.ST 
produces a single data vector whose elements are statistical parameters 
appropriate for circular distributions. These include the length and direction of 
the mean vector (and related measures) as discussed by Batschelet (1). 
Moreover, because the Bugsystem is well suited for investigations of animal 
orientation (and because this is a major interest of one of its codevelopers) we 
have implemented an extensive polar graphics package within the Bugsystem. 
Figure 17-5 illustrates the use of polar wedge histograms to represent angular 
density functions. 
More Advanced Statistical Operations 
These fall into two major categories: operators directed toward the analysis 
of time dependence of behavioral variables and operators used to explore 
mutual relationships between variables (e.g., Figure 17-6). In the First category, 
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