Malmendier and Tate (2008) showed that CEOs classified as overconfident via two observational proxies — holding vested stock options until near expiration and being portrayed as confident in the business press — are 65% more likely to make acquisitions, favor diversifying deals requiring no external financing, and receive significantly more negative merger-announcement returns (−90 versus −12 basis points), with the strongest effects in cash-rich firms. The attribution to overconfidence, however, rests on noisy proxies, and the authors could not fully rule out inside information, signaling, and risk tolerance. The literature since 2008 leaves a precise open core: no study combines a measure of managerial beliefs credibly validated against direct elicitation, quasi-exogenous variation in those beliefs, and causal estimates spanning acquisition propensity through long-run post-merger performance. Partial progress exists on every component — psychometric validation of the option-based measures, survey-based belief elicitations, early-life-experience variation, long-run underperformance evidence, and governance-moderation results — but the conjunction remains open; structural estimation of the misperception parameters needed for welfare and governance counterfactuals remains essentially untouched.

Background

Roll's (1986) hubris hypothesis proposed that takeover bidding is driven by managerial overconfidence — chief executive officers (CEOs) systematically overestimating their ability to run target firms. Malmendier and Tate (2005, 2008) gave this hypothesis its modern empirical form in behavioral corporate finance, the literature that studies how biased managers, rather than biased markets, shape corporate decisions.

CEO overconfidence here means better-than-realistic beliefs about one's own ability, the value of one's own firm, or the synergies a merger will generate. Because beliefs are not directly observed in archival data, Malmendier and Tate (2005) introduced option-based proxies: 'Longholder' flags CEOs who hold vested stock options until (near) expiration, and 'Holder-67' those who leave options at least 67% in the money unexercised after vesting — behavior that is hard to reconcile with a rational, under-diversified executive, who should exercise deep-in-the-money options early. Malmendier and Tate (2008) added a second proxy built from press portrayals of the CEO as confident or optimistic.

The outcome variables follow standard event-study methodology: 'announcement returns' are the cumulative abnormal stock returns of the acquirer in a short window around the merger announcement, measuring the market's assessment of the deal's value creation; long-run performance is typically measured by buy-and-hold abnormal returns (BHARs), the acquirer's realized return over one to three years minus a benchmark, whose sensitivity to benchmark choice is a well-known difficulty. Bertrand and Schoar (2003) showed that managers carry persistent decision 'styles' detectable as manager fixed effects across the firms they run — the design that first made executive-level traits identifiable in panel data.

Malmendier and Tate's (2008) findings: overconfident CEOs are about 65% more likely to make acquisitions, particularly diversifying ones; their bids receive announcement returns roughly 78 basis points more negative than other CEOs' (−90 versus −12 basis points); and the effects are strongest when internal financing is available, consistent with overconfident CEOs also believing their own firm is undervalued and therefore avoiding external finance. The identification caveat is the paper's acknowledged soft spot: option non-exercise could reflect risk tolerance, taxes, diversification needs, inside information about future stock returns, or compensation structure rather than biased beliefs, and 'overconfident' CEOs are not randomly assigned to firms. The paper tests placebo behaviors and alternative interpretations (inside information, signaling, risk tolerance) but cannot exclude them fully.

What would constitute resolution is well defined in the field: a measure of managerial beliefs validated against direct elicitation, an identification strategy producing quasi-exogenous variation in those beliefs, and causal estimates covering both acquisition behavior and long-run outcomes. The 'by how much' half of the question can be answered with credibly identified effect magnitudes, just as Malmendier and Tate (2008) themselves quantified value effects in event-study form. A structural model whose misperception parameters (synergy overestimation versus own-firm undervaluation) are separately estimated would additionally support welfare statements about, for example, governance or contract design, though it is not a condition of resolution. Surveys by the same authors (Malmendier and Tate 2015; Guenzel and Malmendier 2020) treat exactly these measurement, identification, and long-run-benchmarking issues as the field's open agenda.

Problem Statement

The problem left open by Malmendier and Tate (2008) is to convert their proxy-based attribution into an identified and quantified causal account of CEO overconfidence in acquisitions. Overconfidence itself is not observed — it is inferred from delayed option exercise and press characterization, and the source study's own tests cannot fully separate it from inside information, signaling, risk tolerance, or selection. The open problem therefore has two interlocking components that together answer one question: do biased managerial beliefs causally drive acquisitiveness and value destruction in mergers, and by how much?

(1) Belief measurement: construct a measure of CEO beliefs about own-firm value and deal synergies, validated against direct elicitation, that separates overconfidence from ability, risk tolerance, inside information, and tax or diversification motives — the alternative interpretations the 2008 study tested but could not fully exclude.

(2) Causal identification: obtain quasi-exogenous variation in managerial beliefs (a natural experiment, instrument, or research design of comparable credibility) and estimate the causal effects of overconfidence on acquisition propensity, announcement-window returns, and long-run post-merger operating and stock performance beyond the announcement window, addressing the contested benchmarks and missing counterfactuals that the authors' own surveys flag as unsolved.

The 'by how much' half of the question requires credibly identified effect magnitudes.

The question is settled by a belief measure of component (1) validated against direct elicitation, together with causally identified effects of beliefs on acquisition propensity, announcement-window returns, and long-run post-merger operating and stock performance, and by their quantitative magnitude where those effects are nonzero. A credibly identified negative result — showing that the documented effects are attributable to ability, risk tolerance, inside information, or selection rather than biased beliefs — resolves the question on the same footing as a positive result.

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