British American and West African slave prices in pounds sterling 1638-1775
Despite these limitations, the data does show a clear difference between the prices for slaves who were born in the Americas or accustomed to its climate (known as "seasoned"), compared to those who had travelled from West Africa, as those were often weakened from the journey and susceptible to tropical disease, and therefore deemed less valuable. For example, in the period between 1713-17 (the group with the largest sample size), the average value of unseasoned slaves from West Africa was just 38.5% the value of seasoned slaves.