AN-004: Baseline cobidder concentration in FL14 stratum¶
Intuition (plain-language)
Do the firms the screen flags actually cluster on the loser side of adjudicated cartels? Yes — FL14 separates cobidders from other always-losers at AUC 0.924, and the continuous score reaches 0.939 (0.5 is a coin flip). Economically, this says the loser-side concentration a cartel needs in order to fake competition is visible in cheap award records alone, with no bid microdata. This is the headline; everything after it is an attempt to break it with placebos, leakage audits, and timing discipline.
Question¶
Does the FL14 stratum contain a disproportionate share of CADE- adjudication-anchored cobidders relative to the always-loser baseline? This is the headline-baseline triage result.
Design¶
- Sample: 16,843 always-loser firms in BEC 2009–2019.
- Outcome: cobidder indicator (1 if firm is in the 193-firm cobidder set from AN-003).
- Specifications:
- FL14 binary: AUC of the FL14 indicator.
- Continuous: AUC of
log(1 + tenders_count). - Evaluation: in-sample baseline; discipline applied separately in AN-005, AN-006, AN-013, and AN-014.
Results¶
| Score | AUC | 95% CI |
|---|---|---|
| FL14 (binary) | 0.924 | [0.921, 0.926] |
| log(1 + tenders_count) (continuous) | 0.939 | [0.932, 0.946] |
Macros: \valAUCFLfirm, \valAUCFLfirmCI, \valAUClogtc,
\valAUClogtcCI.
Figure: baseline cobidder AUC for FL14 binary (0.924, [0.921, 0.926]) and continuous log(1+tenders_count) (0.939, [0.932, 0.946]). Both substantially above the random benchmark (0.5).
The cobidder share inside FL14 is 7.1% (\valCobidShareFL), against a
baseline always-loser cobidder rate that is much lower. This corresponds
to the headline 131/193 cobidder recovery in the gatekeeping setup
(AN-012).
Interpretation¶
Both the binary and continuous variants concentrate cobidders well inside the always-loser pool. The continuous score is the dominating ranking (AN-011); FL14 is the auditable implementation. The baseline numbers are inflated relative to operational deployment — the disciplined columns in AN-013 and AN-014 are the right operational reading.