δ-presence metric, used to estimate how likely it is for
an attacker to figure out that one given individual appears in a
de-identified dataset. Similarly to the k-map metric, we cannot compute
δ-presence exactly without knowing the attack dataset, so we use a
statistical model instead.
ISO 3166-1 alpha-2 region code to use in the statistical
modeling. Set if no column is tagged with a region-specific
InfoType (like US_ZIP_5) or a region code.
