Misleading Official Statistics on Interdiction and Seizures
"Comparing absolute numbers of total cocaine seizures and manufacture could be misleading. To understand the relationship between the amount of annual seizures reported by States (694 tons cocaine of unknown purity in 2010) and the estimated level of manufacture (788-1,060 tons of cocaine of 100 per cent purity), it would be necessary to take into account several factors, and the associated calculations would depend on a level of detail in seizure data that is often unavailable. Making purity adjustments for bulk seizures, which contain impurities, cutting agents and moisture, to make them directly comparable with the cocaine manufacture estimates, which refer to a theoretical purity of 100 per cent, is difficult, as in most cases the purity of seized cocaine is not known and varies significantly from one consignment to another. The total amount of seized cocaine reported by States is also likely to be an overestimation. Large-scale maritime seizures, which account for a large part of the total amount of cocaine seized, often require the collaboration of several institutions in a country or even in several countries.76 Therefore, double counting of reported seizures of cocaine cannot be excluded."
UNODC, World Drug Report 2012 (United Nations publication, Sales No. E.12.XI.1), pp. 36-37.