Construction of the Trans-Atlantic Slave Trade Database: Sources and Methods
Cases and Variables
New material tends to raise the question of the appropriateness of the variables used. The selection offered here has changed
several times in the last six years and will no doubt change again in the future as interests shift. Each entry in our data set
is a single voyage, assigned a unique identification number as the first of piece of information (VOYAGEID). The question of
what voyages to include is also to some extent arbitrary. The term "trans-Atlantic" is less straightforward than it appears.
Omitting ships sailing to the Mascarene Islands was an easy decision, but several French ships in the late eighteenth century
began their slaving activities in the Indian Ocean, but then on the same voyage brought slaves to the Americas after selling
some Africans in Bourbon and the Cape of Good Hope. What to do with the British ships that carried hundreds of children from
the Upper Guinea coast to Lisbon in the mid-eighteenth century? These we included on the basis of length of voyage. Should
one include the Portuguese trade to São Tomé in the Bight of Biafra—probably the most enduring branch of the Atlantic slave
trade? (excluded on the same basis). Then there were the more than 1,200 slave ships engaged in trans-Atlantic voyages, nearly
half with slaves on board, that the British captured and carried into Sierra Leone, the Cape of Good Hope, St. Helena, Fernando Po,
or Luanda, before they were able to reach their intended American destinations. These we included. Or even more confusing, the
1,060 slaves awaiting shipment in barracoons in Ambriz, Angola, in May 1842, but carried off in British cruisers to St. Helena
and Sierra Leone and never subjected to court proceedings of any kind, because they had never been on board a slave ship (excluded).
Limits had to be established, but the data set provides a basis for those who disagree with those limits to use our work to create their
own data sets. A total of 65 variables are made available on the search the database interface, general category, and 293 variables are
available in the downloadable version of the database. Users should note, though, that the website set combines all sources into one
variable and the day, month, year values are also combined into one variable for each of the ten dates entered. The names of captives,
names of Caribbean agents, names of crew other than captain, the details of shipboard insurrection, and much other information are not
included in the present data set, but may be added fairly easily or linked with it via the unique voyage identification number and
compares version 2008 of the database with version 2010..
The database contains two broad types of variables: data variables and imputed variables. The largest group, 44 of those in the
search interface, are data variables. They incorporate information collected from the sources. Imputed variables, indicated by an
asterisk, are mainly imputed from knowledge of the relevant voyage or adjacent voyages, calculated directly from data encountered
in archival or published sources, or inferred from patterns observed in data variables when not documented directly in primary
sources. An example of an imputed variable is the “Region of Slave Disembarkation Broadly Defined,” a variable that allows one to
group voyages to Jamaica or Cuba or St. Domingue into the broadly defined region “Caribbean.” In augmenting the number of voyages
on which analysis can be conducted, the imputed variables produce more statistically significant results in using the options in
the “Search the database” interface to create tables and custom graphs. They form the basis of the tables and graphs that users can build.