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reports receiving compensation fromMcKinsey & Company for providing strategy consulting to hospitals, insurance companies, and pharmaceutical companies on issues unrelated to this article.

Animal traction constitutes the most important source of power for agricultural work in smallholder farming in Zimbabwe. Two studies, a survey and a short term on-farm trial were conducted to evaluate the use of donkeys as draught animals. The survey covered 59 households in 2 smallholder farming areas. For the on-farm trial, 12 donkeys and 12 cattle were spanned separately in teams of 4 animals to plough 40 m x 70 m plots of medium textured soil. The survey findings highlighted the drought tolerance of donkeys compared to cattle. Mortality rates of donkeys were lower. Results of the draught performance trial indicated that donkeys ploughed less area per day (P < 0.05) and their walking speed was slower (P < 0.05) than cattle. There was no significant difference (P < 0.05) in draught force between the 2 species. The work rate per hour for ploughing with donkeys was 65% of that of cattle. It was concluded that donkeys play a critical role in providing draught power for smallholder farmers but that their potential is not fully utilised.

In hindsight, we realize that we could have been more precise when using the terms 'profit' and 'revenue' in our article 'Low-value approvals and high prices might incentivize ineffective drug development'. Total revenue is defined as the receipts from sales 1. Profit is defined as the excess of the receipts from sales over the spending of a business during any period 1. Hence, profit is the total revenue minus the costs of a business, over a given period. Profit calculations include credit transactions and asset revaluations as well as cash transactions and changes in the value of real assets 1. Nevertheless, this imprecision does not affect the validity of our insight. In our analysis we show that the break-even point for revenue and cost of development (under the specific conditions of our 'thought experiment') would be US$440 million. The annual revenue from the sale of many approved cancer drugs now routinely exceeds $1 billion, and thus we conclude that "pharmaceutical companies could, hypothetically, turn a profit by testing inert chemical compounds in phase III trials". In the conditions we define in our thought experiment, companies would therefore receive sufficient revenues to make a profit.