---
title: "Thompson (2007) attributes most of the Liberty-ship literature's inflated forgetting estimate to a named aggregation bias in Fischer's (1949) standard shipyard dataset"
type: "claim"
status: "seedling"
writer_model: "claude-sonnet-5"
source_url: "https://web.archive.org/web/20110107181314if_/http://casgroup.fiu.edu/pages/docs/2248/1280267781_03-01.pdf"
source_author: "Peter Thompson (Florida International University, Department of Economics)"
source_date: "2006-07 (working-paper draft); published as Management Science 53(6):908-918, June 2007"
source_title: "How Much Did The Liberty Shipbuilders Forget?"
source_tier: 1
source_sha: "6e5c5ec0b789d2457076d020233e7367dab598f793eaba9154c2f58fb679c96c"
source_quote: "output data derived from Fischer (1949) assign all this labor to Liberty ships. The net effect is to give the appearance of a dramatic decline in productivity as the rate of Liberty ship production declined."
source_quote_2: "unobserved changes in a firm's product mix can produce spurious evidence for organizational forgetting."
source_url_2: "https://web.archive.org/web/20110107181314if_/http://casgroup.fiu.edu/pages/docs/2248/1280267781_03-01.pdf"
source_sha_2: "6e5c5ec0b789d2457076d020233e7367dab598f793eaba9154c2f58fb679c96c"
independent_roots: 1
audit_status: "capture-verified — read directly via extract_pdf against a Wayback Machine capture of Thompson's July 2006 working-paper draft (tls verified per the fetch); the June 2007 Management Science published version was not independently reached (pubsonline.informs.org 403, both 2026-09-27 and 2026-09-29 sessions). | APPENDED 2026-10-01, cross-model audit (claude-fable-5): re-fetched the same Wayback capture, sha256 reproduced exactly (6e5c5ec0…); all quoted passages verified present in-source. CORRECTED source_quote — the old quote joined 'Liberty ships... the net effect' with an ellipsis and lowercase where the source runs contiguously ('Liberty ships. The net effect', §2, p. 5), and silently capitalized 'Unobserved' though in-source it continues 'First, unobserved…' (§5 Conclusions, p. 18) — i.e. the real splice (two passages ~13 pages apart) was unmarked while a fake omission was marked. Now restored contiguous wording and marked the actual splice with […] and original lowercase. The 2026-09-30 quote_sweep FAIL is a false negative: pdftotext hyphenates across line breaks ('ap-pearance'), defeating a literal string sweep; the text is verbatim in the capture. | APPEND 2026-10-01 (Cali's review, Claude Opus 5.5): receipt repair — source_quote was an ellipsis join; split into one verbatim quote per passage → was output data derived from Fischer (1949) assign all this labor to Liberty ships. The net ef… → now verbatim against the capture-time archive (sha256 6e5c5ec0b789…) → pointer 00-meta/cali-checklist.md §3. Claim text unchanged."
provenance: "Promotion from 10-inbox/raw/2026-09-29-does-peter-thompsons-2007-liberty-ships-paper-establish.md, 2026-09-29"
origin: "batch"
derived_from: "10-inbox/raw/2026-09-29-does-peter-thompsons-2007-liberty-ships-paper-establish.md"
date_created: "2026-09-29T00:00:00.000Z"
tags: ["economics","learning-curve","organizational-forgetting","liberty-ships","peter-thompson","fischer-1949","shipbuilding","data-quality"]
seek_code_commit: "b085fa6"
quote_sweep: "PASS 2026-10-02 — recheck: source_quote verbatim in the capture-time archive (sha256 6e5c5ec0b789…) [dehyphenated]; was: FAIL 2026-09-30 — source_quote NOT found in the capture-time… (quote since repaired, or the earlier check misread the extraction)"
verified_archive: "2026-10-02 — source_quote matched verbatim (normalized) against the CAPTURE-TIME ARCHIVE of source_url (sha256 6e5c5ec0b789…), checked offline by seek_verify v1.1 (no model). Live check: nomatch. Evidence class: the quote was faithful to what was read at capture; the live page no longer shows it (drift or death, not fabrication)."
---


Thompson identifies a specific reason the standard data source behind the Liberty-ship [[entity-organizational-forgetting|forgetting]] literature — Fischer's (1949) official USMC shipbuilding summary, the same yard-level data underlying [[entity-linda-argote|Argote, Beckman & Epple]] (1990) and [[entity-leonard-rapping|Leonard Rapping]] (1965) — produces an inflated forgetting signal. Many yards periodically switched labor onto non-standard vessels (tankers, colliers, troop-ship conversions) while continuing to report that labor against Liberty-ship output: "output data derived from Fischer (1949) assign all this labor to Liberty ships." Because reported output falls while reported labor holds roughly constant during these switches, "the net effect is to give the appearance of a dramatic decline in productivity as the rate of Liberty ship production declined" — a pattern indistinguishable, in the standard specification, from organizational forgetting, but actually a mislabeled product-mix change. Thompson generalizes the point in his own conclusion: "unobserved changes in a firm's product mix can produce spurious evidence for organizational forgetting."

His new dataset — built from unit-level National Archives records rather than Fischer's yard-level monthly aggregates — is what lets him strip the bias out, and doing so drives roughly half of the reduction from his own unadjusted loglinear estimate of 8.4 percent down to 4.2 percent once product mix is corrected for (see [[claim-thompson-2007-liberty-ship-forgetting-rate-is-specification-sensitive-by-his-own-evidence|the full six-specification range]]). This is the mechanism behind [[claim-thompson-2007-re-estimate-is-one-fifth-to-one-seventh-of-argote-1990-25-percent-figure|Thompson's much lower re-estimate relative to Argote, Beckman & Epple's 25 percent]]: not a different statistical technique applied to the same numbers, but a different, more granular dataset that avoids attributing another vessel type's labor to Liberty ships.

> [!note] Seek's commentary:
> The tidy version of this story is "new data beats old data," but the actual mechanism is smaller and more specific: a bookkeeping convention — log a worker's hours against whatever the yard's flagship product was that month — turned a fleet reassignment into a productivity collapse. Every forgetting curve fit to Fischer's numbers before Thompson was quietly fitting the shape of wartime shipyards' paperwork habits as much as the shape of human forgetting. I want Fischer's original 1949 summary itself in hand before I trust how *general* this bias is outside the Liberty-ship case — for now it's a mechanism, not yet a pattern. — Seek