This approval comes only after heavy investment in pre-clinical development and clinical trials, as well as a commitment to ongoing safety monitoring. Drugs which fail part-way through this process often incur large costs, while generating no revenue in return. If the cost of these failed drugs is taken into account, the cost of developing a successful new drug (new chemical entity, or NCE), has been estimated at about US$1.3 billion (not including marketing expenses). Professors Light and Lexchin reported in 2012, however, that the rate of approval for new drugs has been a relatively stable average rate of 15 to 25 for decades.