Construction of the Trans-Atlantic Slave Trade Database: Sources and Methods

David Eltis (Emory University), 2010

Data Variables

The variables include information that, for convenience, have been grouped into eight categories: (1) vessel characteristics (name, tonnage, rig, guns, place and year of construction, owners); (2) the outcome of the voyage (3) the itinerary of the voyage; (4) the dates at which the vessel left or arrived; (5) the captain and crew of the vessel; (6) the numbers of captives; (7) the characteristics of the captives and their experience of mortality; and (8) the sources for the record. The Variable List in the “Understanding the Database” section presents a complete listing of the data variables as well as the imputed variables in the data set. Imputed variables are always marked with an asterisk. No voyage, however, includes information for all data or imputed variables. Table 1 provides a summary of the coverage for some of the more important data variables.

Generally, we attempted to preserve the written documentary record in adding to the data variables. Numeric variables, such as vessel tonnage, numbers of crew, and numbers of slaves, demanded a ranking of sources, particularly for the well-documented British trade. (5)

Table 1. Select Summary of Information Contained in the Trans-Atlantic Slave Voyage Data Set: Version 2008 Compared to 2010

2008 2010
Number of slave voyages in the data set 34,940 34,948
Voyages with name of vessel 33,337 33,353
Voyages with name of captain(s) 30,895 30,894
Voyages with name of at least one ship owner 21,024 21,064
Tonnage of ship available 17,691 17,608
Place of ship departure given 28,443 28,449
Date of ship departure given 22,193 22,231
Place(s) of embarkation on the African coast available 21,121 21,291
Numbers of Africans embarked reported 8,207 8,272
Voyages with age or gender of Africans reported 4,426 4,498
Place(s) of disembarkation available 24,849 24,916
Dates of arrival at place of disembarkation available 17,446 17,533
Numbers of Africans disembarked reported 18,184 18,269
Voyages reporting number of Africans died on board 6,332 6,438
Voyages with place of ship construction reported 8,881 8,888
Date of return to Europe or end of voyage given 10,100 10,414
Some indication of outcome of voyage indicated 31,554 31,612

Sources often report different numbers of slaves embarked on or "taken on board" the coast of Africa or landed in the Americas. Furthermore, for some years there are inconsistencies in slave age or gender totals per voyage. Regarding slave exports, we were careful to distinguish between the number of slaves purchased and the number who in fact were shipped from the coast. We used slave departure totals, whether reported by slave traders, African merchants, or European captains, agents, or merchants. We included the slave departures reported in sources such as logs kept by the Dutch and English castles on the Gold Coast, even though the totals often were rounded numbers, such as 400 or 500 slaves, and even though the totals occasionally were significantly less than the numbers of slaves who were disembarked in the Americas. Users should keep these biases in mind, not least for any calculations of mortality they may wish to try. For slave arrivals recorded in customs documents or shipping gazettes, we decided to use maximum totals where there was conflicting information, under the assumption that these differences might indicate deaths of slaves before slaves disembarked.

Cases and Variables Age Categories
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