Compare methods

	Historical GDP Back-Projection	Occupational Structure Reconstruction
Field	Economic History	Economic History
Family	Process / pipeline	Process / pipeline
Year of origin	2001	2010
Originator	Angus Maddison; with indicator methods from Robert Allen, Paolo Malanima, and Jan Luiten van Zanden	E. A. Wrigley and the Cambridge Group for the History of Population and Social Structure
Type	descriptive-extrapolation	descriptive-reconstruction
Seminal source	Maddison, A. (2007). Contours of the World Economy 1-2030 AD: Essays in Macro-Economic History. Oxford University Press. ISBN: 9780199227204	Wrigley, E. A. (2010). The PST System of Classifying Occupations. Cambridge Group for the History of Population and Social Structure.
Aliases	Maddison back-projection, Indicator-based GDP estimation, Retrospective GDP extrapolation, Benchmark-and-interpolation GDP	PST occupational coding, Sectoral structure reconstruction, Primary-secondary-tertiary classification, Cambridge occupational structure
Related	3	3
Summary	Historical GDP back-projection estimates long-run income for periods too thinly documented for full national accounting. Rather than rebuilding sectoral value-added year by year, it anchors to a handful of relatively secure benchmark estimates and fills the gaps between and before them using indirect indicators that move with income, chiefly the share of population living in towns, real wages of building labourers, agricultural productivity, and population density. The logic, associated above all with Angus Maddison and developed further by Allen, Malanima, and van Zanden, is that these indicators bear a stable, theoretically grounded relationship to per-capita output, so their movements can proxy GDP growth where direct measurement is impossible. The method has produced the multi-century per-capita income series that frame debates about pre-modern stagnation, Malthusian dynamics, and the European Little Divergence, while remaining explicitly more uncertain than bottom-up accounts.	Occupational structure reconstruction uses the distribution of the workforce across economic activities to chart how an economy's sectoral composition evolved before modern statistics. The Cambridge Group, led by E. A. Wrigley, developed the Primary-Secondary-Tertiary (PST) system, a classification purpose-built for historical occupational descriptors that sorts every recorded occupation into agriculture and extraction (primary), manufacturing and processing (secondary), or trade, transport, and services (tertiary), with finer subdivisions beneath. By coding occupations from censuses, parish registers, probate inventories, trade directories, and militia lists, the method estimates the share of workers in each sector and tracks its movement across benchmark years. Because the shift from primary to secondary and tertiary employment is the structural signature of economic development, these reconstructions illuminate the timing and geography of industrialization with a directness that aggregate output figures cannot match, complementing and constraining national-accounting estimates of growth.