
Construction of the TransAtlantic Slave Trade Database: Sources and Methods
David Eltis
(Emory University),
2010
Age and Gender Ratios
As noted above in description of data variables for “Age categories,” they do provide enough
information to describe in gross terms the demographic structure of the trade—the age and gender
composition of the Africans carried off as slaves. For 93 voyages, age and sex data is available
for up to three places of embarkation and two places of landing of slaves, and for 437 voyages
information exists on the age and gender of slaves who died on the crossing. When available,
the quality of the data varies considerably. The most precise data is for 3,404 voyages with
records that report the number of “men,” “women,” boys,” and ”girls,” as well as in some cases
“children” and “infants.” For another 811 voyages, the number of “adults” and “children” are
distinguished without indication of their gender; while 484 voyages reported the number of “males”
and “females” they carried without specifying how many were adults and children.
Several age and gender variables were imputed from the data variables. First, information
from voyages with more than one place of embarkation and/or disembarkation of slaves was aggregated
to produce one set of four variables – adults, children, males, and females – for places of departure
and another for places of arrival. An additional set of the same variables was calculated for deaths on
the Middle Passage. From these variables, we calculated two ratios: the proportion of children for all
voyages with information on adults and children, and the proportion of males for all voyages with information
on males and females. The proportion of adults and females are the reciprocals of the variables that were
computed. The ratios are to be understood as the proportion of all slaves for whom a characteristic can
be determined. The child ratio is the percentage of slaves identified as either children or adults,
and the male ratio is the percentage of slaves identified as males or females. For the smaller
number of voyages with information on both age and gender, we also calculated the ratios of men,
women, boys, and girls. Ratios were imputed only for voyages with at least 20 slaves whose
age and/or gender is documented.
Each ratio was calculated for places of departure, arrival, and deaths; but to further simplify
the information for inclusion in the set of variables available on the Voyages website, one set of
ratios is provided for each voyage with age and sex information. It is the same as the proportion
at arrival when that is documented; otherwise it is the proportion at departure. The age and sex of
captives was recorded almost two times more often at places of landing (3,731 voyages) than it was at
places of embarkation (1,970 voyages). Information on the demographic composition of slave cargoes at
both embarkation and disembarkation exists for only 609 voyages.
Caution is required in inferring age and gender patterns from the ratios.
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 enough numbers of cases, this problem diminishes to the point of becoming
negligible; 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 voyagebased 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. 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 may obtain somewhat different results from those
provided in the search interface, but they will have to first download the database to
make that calculation.
Users should also remember that age and sex information was recorded on some vessels
at the beginning of the voyage and on 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
of data, and where information has survived on both we gave precedence to the ratios at the point
of disembarkation. This procedure is justified by the finding that shipboard mortality was only
modestly age and sex specific. Those users who wish to eliminate these modest effects should
download that database first.(12)
 