dcr: Distance to closest record (disclosure risk)

In SynthesizerPlus: Synthetic Data Generation with Copulas, Evaluation and Multi-Format I/O

Distance to closest record (disclosure risk)

Description

For every synthetic record (in a subsample of at most max_rows), the Gower distance to the closest real record is computed. As a baseline the same is done for real records with respect to the other real records. Synthetic records that are much closer to real records than real records are to each other, and in particular exact copies (distance 0), indicate a disclosure risk.

Usage

dcr(
  real,
  synthetic,
  vars = NULL,
  max_rows = 2000L,
  seed = NULL,
  close_quantile = 0.05,
  na = c("category", "exclude")
)

Arguments

real, synthetic	Data frames with common columns.
vars	Optional subset of variables.
max_rows	Maximum number of records used from each data set.
seed	Optional random seed (subsampling).
close_quantile	Quantile of the real-to-real distances that defines a synthetic record as "too close" to a real record (see close_share).
na	Treatment of missing values: "category" (default) or "exclude" (standard Gower); see Details.

Details

Numeric variables contribute their absolute difference divided by the range in the real data, categorical variables 0 (equal) or 1 (different). Missing values are handled according to na:

• "category" (default): missingness is treated as a category of its own – two missing values match, a missing and an observed value differ – and the distance is averaged over all variables. Because the synthesizer reproduces missingness patterns, and an intruder sees them, this is the appropriate view for disclosure risk.

• "exclude": the standard Gower (1971) coefficient; a variable missing in either record is left out of the comparison and the distance is averaged over the variables observed in both. Records with no variable in common have no distance (NA) and are ignored.

Value

A list with the distance vectors synthetic and real, their quantiles, the share of synthetic records that are exact copies of a real record on all variables (exact_match_rate), the share at distance zero on the variables compared (zero_distance_rate; with na = "exclude" this can include records that agree with a real record only on the few variables observed in both), the average share of variables on which the nearest real record was compared (compared_share; always 1 with na = "category"), the share of exact duplicates within the real data (real_duplicate_rate) and ratio, the median synthetic distance divided by the median real-to-real distance (values well below 1 are a warning sign), and close_share, the share of synthetic records that are closer to a real record than close_quantile (5\ are to their nearest real neighbour. For synthetic records that are as far from real ones as real records are from each other, close_share is about close_quantile; larger values indicate records that may be recognised as near-copies of real persons.

References

Gower, J. C. (1971). A general coefficient of similarity and some of its properties. Biometrics, 27(4), 857–871. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.2307/2528823")}

Examples

syn <- synthesize(iris, seed = 1)
str(dcr(iris, syn, seed = 1)[c("exact_match_rate", "ratio")])

# data with missing values: missingness as a category, or standard Gower
aq <- synthesize(airquality, seed = 1)
dcr(airquality, aq, seed = 1)$ratio
dcr(airquality, aq, seed = 1, na = "exclude")$ratio

SynthesizerPlus documentation built on Oct. 16, 2026, 5:10 p.m.