overlap_fc: A fraction check for overlap.

In divoRce: Diagnosing Separation Phenomena in Categorical Response Models

A fraction check for overlap.

Description

Intended for data where one suspects overlap, this function checks for overlap on an ever growing subset of the data. It is a low-level function for a response vector y and a design matrix X.

Usage

overlap_fc(
  y,
  X,
  S,
  frac = 10L,
  verbose = FALSE,
  rational = FALSE,
  model = c("b", "bcl", "cl", "acl", "sl", "osm"),
  backend = c("rcdd", "ROI"),
  solver = NULL
)

Arguments

y	outcome vector.
X	design matrix.
S	structure vector matrix
frac	the fraction of the data to use for checking (uses n/frac data). Defaults to 10. If frac is below 1 or n, it uses frac=1. Using frac=1 is the same as using checkovl.
verbose	should progress be reported. Defaults to 'FALSE'.
rational	should rational arithmetic be used?
model	what model class is intended to be fitted? Can be any of "b" for binary, "bcl" for baseline-category link, "cl" for cumulative link, "acl" for adjacent-category link. "sl" for sequential link, "osm" for ordered stereotype model. If missing it defaults to cumulative link for ordinal y and baseline-category for everything else.
backend	which backend to use for the linear program. Can be 'rcdd' (default and only option for rational=TRUE) or 'ROI'.
solver	the solver to be used in the backend. Defaults to "DualSimplex" for "rcdd" and the first LP solver returned by 'ROI_applicable_solver()' for "ROI".

Details

The function samples a fraction of observations form the data and checks for overlap. If overlap exists in a subset, then overlap exists in the overal data (Sablica et al,. 2026). If no overlap is found, it takes a larger sample and checks again until all data are tested. If no overlap is found even for all data, it concludes there is separation.

Since solving the exact linear program on the full data via checkovl can take a long time for large data, this check can be quicker in case of overlap (especially if the overlapping categories are not rare). However, if there is separation this function usually takes longer.

Value

a Boolean; either 'TRUE' if we detect overlap or 'FALSE' if we do not (so the data show separation).

divoRce documentation built on April 28, 2026, 3:01 a.m.