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

Imputed Voyage Dates

There are also imputed variables for both voyage dates and on numbers of captives. Because most slaving voyages lasted for many months or even years, and no voyages have complete information for all ten date variables, we have created three definitions of "year" in the full downloadable database from which users can choose for purposes of analysis: the year in which the voyage originated, the year of embarkation of slaves, or the year of arrival at point of disembarkation. In the Voyages Database only “YEARAM” or “year of arrival” is provided. We created imputed year values when the sources did not record the years when voyages departed their homeport, or departed the African coast, or the year when vessels arrived in the Americas. If a London-based vessel arrived in Jamaica in September 1770, for example, the year 1770 becomes the imputed African departure year, and the year 1769 becomes the imputed departure year from the homeport. Further, years of arrival in the Americas are grouped into periods of five, twenty-five, fifty, and one hundred years. For the numbers of slaves carried and the numbers who perished during the voyage, as well as the age and gender categories, information is also frequently incomplete and additional imputed values are added, the creation of which is discussed more fully below. Researchers can of course make their own estimates and these, like the inferences on which alternative estimates are based, may well be different from what we regard as optimal. We would like to emphasize that in many cases the optimal solution is not obvious, and one researcher’s estimates (and inferences) may be different from, but as good as, another’s, despite the fact that all are working with the same data set. Anyone using the data, including ourselves, therefore needs to specify clearly the assumptions he or she is using.