Price data may differ from data as reported due to conversions made by UNODC. Prices are collected in local currency but are presented here in US dollars for the purposes of comparability among countries. The conversion into US dollars is based on official UN rates. However, comparisons of prices from different years need to be made with caution as they are influenced by changes in the exchange rates and may not necessarily reflect changes in the local markets. While the same price can be meaningfully expressed in various units (e.g. per kilogram, per gram), the purchase unit as presented here (and as requested in the ARQ) is intended to approximate, to the extent allowed by the availability of information, the level at which transactions occur; thus a retail price, for example, would normally be expressed per gram even if reported per kilogram. On the other hand, the reporting unit is not converted if it is believed to represent the actual transaction level, except that non-standard units are converted when possible to the nearest available metric unit.