In the domain of pharmaceuticals, we need a metric for health impact, and with this metric we can then assess the value of the introduction of a new product and pay its innovator accordingly, say on the basis of the product's measured health impact during its first ten years on the market. In exchange, innovators must of course renounce the usual rewards they are otherwise entitled to, namely the patent-protected markup on the price of their product.

Over the period from 1988 to 2005, the income share of the top five percent has grown by about 3.5 percent of global household income, and the shares of all the other groups have diminished. The greatest relative reduction was in the bottom quarter, which lost about one third of its share of global household income, declining from 1.155 to 0.775 percent, and now is even more marginalized.

Think of US slavery in 1850, or the subjection of women. Both of these injustices could have been - and were! - defended by pointing out, quite correctly, that this situation of slaves and women had been improving throughout the preceding century. Slaves, in particular, were worked less hard, beaten and raped less frequently, better fed, and less often ripped apart from their families. So would a celebration of moral progress have been appropriate in 1850? Surely not. Slavery could have been and should have been abolished - then, if not before.

To make a proper moral appraisal of the prevalence of severe poverty today, we should focus not on comparisons with times past, when the global average income was much lower, but on a comparison with what would be possible in our time, given the current global average income and level of technological and administrative development.

For the present system to work, poor people must be excluded from the innovation, because if they could get access at an affordable price, then affluent people would find ways to buy it cheaply as well - and then the innovator would be poorly rewarded and introductions of new medicines would decline.

We live in a world where economic positions - income and wealth - are very unevenly distributed, and this leads to the widespread persistence of poverty.

Income inequality matters more on a day-to-day basis. Wealth matters more for political influence.