def big_cohort(characteristics, options = {})
      BigCohort.new self, characteristics, (options[:minimum_cohort_size] || (klass.respond_to?(:minimum_cohort_size) ? klass.minimum_cohort_size : nil))
    end
def big_cohort(characteristics, options = {})
      BigCohort.new self, characteristics, (options[:minimum_cohort_size] || (klass.respond_to?(:minimum_cohort_size) ? klass.minimum_cohort_size : nil))
    end
Find the biggest scope possible by removing characteristics <b>in any order</b>.
 Returns an empty scope if it can't meet the minimum scope size.