Candidate combination,P(collision),Secondary risk category,Why the risk is not fully captured by P(collision)
Date of Birth + Street Address + ZIP,3.00E-13,Twin risk; shared living space risk,"Twins, siblings in the same household, and residents in shared or institutional settings may share these fields; address standardization can also collapse distinctions if unit information is missing or inconsistent"
Email + Date of Birth + City + State,1.00E-12,Shared contact channel risk,"Email addresses may be shared by spouses, parents, guardians, or caregivers; City and State add limited incremental discrimination"
First Name + Last Name + Street + Zip,3.00E-13,Shared contact channel risk; Generational Name risk,Parent and child generational names in the same household where suffix was either not disclosed or not transmitted
Phone + City + State + Zip,1.8E-13,Reassignment risk; Shared contact risk; Data independence risk,"Though clearly under the threshold, phone numbers are frequently shared or reassigned. City, State, and Zip are not independent."
First Name + Last Name + DOB + ZIP,3e-12 (framework),Above threshold; geographic dependency question,"With Table 3 u-values this combination yields P(collision) = 3e-12, which exceeds the 2e-12 threshold and is ineligible for approval without a formally documented dependency adjustment. The value 3e-13 appears in some prior analyses of this combination, suggesting an implicit discount is being applied to correlated geographic and demographic fields; that discount must be specified and validated before this rule may be reconsidered."
Last Name + DOB + City + ZIP,1.5e-12 (framework),Data independence risk,"City and ZIP are correlated fields — ZIP already encodes city and state. Per §IV.D assumptions, the combination should not receive full independent credit for both. A dependency adjustment reducing the effective contribution of City is warranted before this rule is approved, and the adjusted value should be validated against population data per §IV.F."