Learning and Liberty Ships, P. Thompson

(Note: This post refers to “How Much Did the Liberty Shipbuilders Learn? New Evidence for an Old Case Study” (2001) and “How Much Did the Liberty Shipbuilders Forget?” (2007), both by Peter Thompson.)

It’s taken for granted now that organizations “learn” as their workers gain knowledge while producing and “forget” when not actively involved in some project. Identifying the importance of such learning-by-doing and organizational forgetting is quite a challenging empirical task. We would need a case where an easily measurable final product was produced over and over by different groups using the same capital and technology, with data fully recorded. And a 1945 article by a man named Searle found just an example: the US Navy Liberty Ships. These standardized ships were produced by the thousand by a couple dozen shipyards during World War II. Searle showed clearly that organizations get better at making ships as they accumulate experience, and the productivity gain of such learning-by-doing is enormous. His data was used in a more rigorous manner by researchers in the decades afterward, generally confirming the learning-by-doing and also showing that shipyards which stopped producing Liberty ships for a month or two very quickly saw their productivity plummet.

But rarely is the real world so clean. Peter Thompson, in this pair of papers (as well as a third published in the AER but discussed here), throws cold water on both the claim that organizations learn rapidly and that they forget just as rapidly. The problem is two fold. First, capital at the shipyards was assumed to be roughly constant. In fact, it was not. Almost all of the Liberty shipyards took some time to gear up their equipment when they began construction. Peter dug up some basic information on capital at each yard from deep in the national archives. Indeed, the terminal capital stock at each yard was three times the initial capital on average. Including a measure of capital in the equation estimating learning-by-doing reduces the importance of learning-by-doing by half.

It gets worse. Fractures were found frequently, accounting for more than 60% of ships built at the most sloppy yard. Speed was encouraged by contract, and hence some of the “learning-by-doing” may simply have been learning how to get away with low quality welding and other tricks. Thompson adjusts the time it took to build each ship to account for an estimate of the repair time required on average for each yard at each point in time. Fixing this measurement error further reduces productivity growth due to learning-by-doing by six percent. The upshot? Organizational learning is real, but the magnitudes everyone knows from the Searle data are vastly overstated. This matters: Bob Lucas, in his well-known East Asian growth miracle paper, notes that worldwide innovation, human capital and physical capital are not enough to account for sustained 6-7% growth like we saw in places like Korea in the 70s and 80s. He suggests that learning-by-doing as firms move up the export-goods quality ladder might account for such rapid growth. But such a growth miracle requires quite rapid on the job productivity increases. (The Lucas paper is also great historical reading: he notes that rapid growth in Korea and other tigers – in 1991, as rich as Mexico and Yugoslavia, what a miracle! – will continue, except, perhaps, in the sad case of Hong Kong!)

Thompson also investigates organizational forgetting. Old estimates using Liberty ship data find worker productivity on Liberty ships falling a full 25% per month when the workers were not building Liberty ships. Perhaps this is because the shipyards’ “institutional memory” was insufficient to transmit the tricks that had been learned, or because labor turnover meant good workers left in the interim period. The mystery of organizational forgetting in Liberty yards turns out to have a simpler explanation: measurement error. Yards would work on Liberty ships, then break for a few months to work on a special product or custom ship of some kind, then return to the Liberty. But actual production was not so discontinuous: some capital and labor transitioned (in a way not noticed before) back to the Liberty ships with delay. This appears in the data as decreased productivity right after a return to Liberty production, with rapid “learning” to get back to the frontier. Any estimate of such a nonlinear quantity is bound to be vague, but Peter’s specifications give organizational forgetting in Liberty ship production of 3-5% per month, and finds little evidence that this is related to labor turnover. This estimate is similar to other recent production line productivity forgetting estimates, such as that found in Benkard’s 2000 AER on the aircraft industry.

How Much did the Liberty Shipbuilders Learn? (final published version (IDEAS page). Final version published in JPE 109.1 2001.

How Much did the Liberty Shipbuilders Forget? (2005 working paper) (IDEAS page). Final paper in Management Science 53.6, 2007.

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