Seventeenth-century slave voyages probably killed about 20 percent of the slaves. During the eighteenth century, modest improvements in food, water, and cleanliness gradually cut the mortality rate in half to about 10 percent by the 1780s. Nonetheless, a 10 percent mortality was still a high rate for a population of young men, ordinarily the healthiest group. By comparison, only about 4 percent of the English convicts died during their passages across the Atlantic.
