IMPORTANT NOTE
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Version 2.4.4 of the PE Toolbox changes an important internal parameter in the hd-PS variable selection process.  
In prior versions, a code had to occur at least 100 times across the population in order to be considered for inclusion.  
This version removes that requirement, but to maintain compatibility with older versions, a minimum frequency can be 
imposed by setting the option:

	frequency_min = 100
	
Other values of minimum frequency can also be set as desired.  
Setting the minimum to 0 indicates that no minimum threshold must be met.