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

Age and Gender Ratios

As already noted, the demographic structure of the trade—the age and gender composition of the Africans carried off as slaves—is well represented in the data grouping of variables. Some modest inferences, however, are required to present an accurate picture of any age and gender pattern that requires computations of two or more voyages. Ships left the African coast with varying numbers of men, women and children on board. It makes little sense to combine, say, the Merced, taken into Sierra Leone with only one man slave on board, and the Alerta, which landed 69 men among 606 slaves disembarked in Havana in September 1818. The ratio of men in the first voyage was 100 percent, the ratio in the second case was 11 percent. Averaging without any further adjustment produces a ratio of men of 56 percent, which, given the different numbers of people on board, misrepresents historical reality. With large numbers of cases, this problem will tend to be unimportant, but if users select a small number of cases, they should employ a simple weighting technique to correct for the differences in the number of people being counted. Thus, in the above example, the weighted average of men on the two ships is very much closer to the 11 percent on the Alerta than the 100 percent on the Merced. Alternatively, users might disregard our voyage-based age and gender ratios and simply divide the total of males (or females) by the total number of slaves in the sample they select. As the above discussion suggests, the ratios for age and sex made available in the Voyages Database are calculated without weighting. Thus, for example, “Percentage male*” (MALRAT7) is computed by averaging the ratios computed for each voyage. Thus a mean of, say, 70 percent male for a group of years or a region is the unweighted average of male ratios for individual voyages in the selected group. If users wish to group all males in the selection (or all children) and divide by all slaves, they will most likely retrieve a different result from that provided in the search interface, but they will have to first download the database to make that calculation.

Users should also note that age and sex information was recorded on some vessels at the beginning of the voyage and others at the end of the voyage. We have created composite male and child ratio variables, “Percentage male*” (MALRAT7) and “Percentage children*” (CHILRAT7) that lump together information from both ends depending on availability, and where information has survived on both we gave precedence to the ratios at the point of disembarkation. This procedure was justified by the fact that shipboard mortality was only modestly age and sex specific, and those users who wish to eliminate these modest effects should download that database first.(12)