David Ricardo

In comparing therefore the value of the same commodity, at different periods of time, the consideration of the comparative skill and intensity of labour, required for that particular commodity, needs scarcely to be attended to, as it operates equally at both periods.

A health system that lacks commodities for managing high-mortality infectious diseases and the main killers of mothers and young children will not have an adequate impact. By the same token, even the best-stocked delivery system will have an inadequate impact if it fails to reach the poor.