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   "estimand": "Distribution across borrowers of walk-away (threshold) negative equity / CLTV levels at which ruthless default occurs",
   "strategy": "Two steps: a discrete-time logit hazard model of default on flexible CLTV dummies, exploiting ZIP-level variation in the timing and size of house price declines among zero-down-payment borrowers; then maximum likelihood estimation of a gamma distribution of default costs, with defaults probabilistically classified as liquidity-driven or ruthless.",
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    "Default arises only from unwillingness to pay (an equity response) or inability to pay (liquidity)",
    "The effect of equity on default can be separated from liquidity shocks once loan-age fixed effects, quarter fixed effects and county economic conditions are controlled",
    "ZIP-code HPI accurately measures individual home equity",
    "Borrowers walk away when the financial benefits exceed the costs"
   ],
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    "liquidity/income shocks confounding default timing",
    "endogenous down payment choice (all borrowers start with CLTV of 100)",
    "lender recourse",
    "measurement error in house values",
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   "convention_notes": "Notes describe the estimating equation, the number of observations and the fixed effects that are included but not shown. The logit table reports coefficients, standard errors and odds ratios. Walk-away distributions are reported as CLTV percentiles (25th, median, 75th) with N, and the baseline row is repeated across the mechanism, robustness and broader-sample tables.",
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   {
    "claim": "Median borrower does not walk away until CLTV reaches about 174 (equity of -74%)",
    "evidence_type": "table",
    "evidence_ref": "Table III; Figure 7"
   },
   {
    "claim": "CLTV alone does not drive default until it exceeds roughly 120",
    "evidence_type": "table",
    "evidence_ref": "Table II; Figure 6"
   },
   {
    "claim": "Frictionless option model predicts certain default at about -20% equity",
    "evidence_type": "prior_literature",
    "evidence_ref": "Kau, Keenan, and Kim (1994)"
   },
   {
    "claim": "Lender recourse is not the main driver of high walk-away thresholds",
    "evidence_type": "table",
    "evidence_ref": "Table IV"
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   {
    "claim": "High thresholds also hold in a broader sample including GSE and portfolio loans",
    "evidence_type": "table",
    "evidence_ref": "Table VI"
   },
   {
    "claim": "House prices fell sharply in the four studied states",
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    "evidence_ref": "Figures 1-2"
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  ],
  "structural_summary": "The introduction moves from the crisis facts to the ruthless-default debate, then previews the headline magnitude against model predictions. It defends a two-step method that separates liquidity-driven from ruthless defaults and closes with policy implications on moral hazard. A short conceptual section defines ruthless default, followed by the data section. The empirical section estimates a hazard model and then a maximum likelihood distribution of walk-away thresholds. A long discussion section weighs financial versus behavioral mechanisms, identification, external validity and robustness. The conclusion restates the findings and leaves the behavioral drivers to future research.",
  "writing_profile_keywords": [
   "walk-away threshold",
   "negative equity",
   "hazard model",
   "maximum likelihood",
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   "policy implication",
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  "notes": "Primary method could also be classed as reduced_form_regression, since step 1 is a logit hazard; it was labelled structural because step 2 estimates a parametric default-cost distribution by maximum likelihood. The Discussion section's role_rule says conclusion, but its content is mechanisms and robustness, so it was assigned robustness. The way statistical significance is reported is not visible in the excerpts."
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