With US government cooperation, the Peruvian Government installed the National Plan for the Prevention and Control of Drugs in 1995. This government prohibition of narcotics trafficking in Peru has resulted in a 70% reduction of coca leaf cultivation since 1995. However the reduction in cultivation may not have actual effects on cocaine production, as recent advances in coca growing and more efficient processing methods allow for greater cocaine yield. The size of the narcotics industry as a part of the national economy is difficult to measure, but estimates range from $300–$600 million. An estimated 200,000 Peruvian households have economies based on the production, refining, or distribution of coca. Many economists believe that large flows of dollars into the banking system contribute to the traditional depression of the dollar exchange rate vis-a-vis the sol. The Central Bank engages in open market activities to prevent the price of the sol from rising to levels that would cause Peruvian exports to become prohibitively expensive.