A string of the form "#.#" or "#.#.#" specifying a SaTScan
parameter set. If this parameter is NULL or not specified, then parameters
are reset based on the latest version of SaTScan.
This parameter defines which parameter set the script uses,
not necessarily the version of SaTScan being used to execute the analyses.
SaTScan is backwards compatible with older versions of parameter sets.
For instance you might create a script that uses the 10.1 parameter set.
That parameter set in the script will continue to work as you upgrade your SaTScan
executable to newer versions. This is the same way that rsatscan worked up to version 1.0.3
where the script was locked to the 9.2 parameter set but you still could use SaTScan 9.3,
9.4, 9.7, 10.1, etc without access to the newer parameter set options introduced in
those versions. As such, users with scripts created with rsatscan prior to version 1.0.4
must explicitly set the parameter set version in their scripts.
The parameter sets are stored in the 'ssenv' environment object.
WARNING: Clearing your R environment will delete the 'ssenv' object and cause an error
when attempting to use any SaTScan parameter sets. The 'rsatscan' library must
be reloaded to restore the 'ssenv' object and allow SaTScan parameters to work
correctly.