It is also possible to construct studies which calculate aggregate statistics across multiple sites.  A user should be able to see his/her own site's statistics, but not be able to calculate or deduce the statistics for any other site.  From this security basis comes the 3-in, 3-out rule : no region for study can be considered unless at least three sites are included and three sites excluded in every intersection and union with all other regions.    In the example above, the circles represent defined regions. They are all legal because no subregion created by intersecting or unioning regions includes 1 or 2 regions.  If doing so included only one region, it would be possible to calculate the statistics for that region, and if doing so included only 2 regions, it would be possible for each of those regions to calculate the statistics for the other.  This way, it is possible to calculate the statistics for a general region (e.g., a state) without knowing the specifics of any site other than the user's own. next Please contact us for more information.

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